Whether those stories can be turned into successful movies luckily isn't my problem.
No, but it is WotC's problem, and if you're arguing that they could succeed, failing to address it is a problem. D&D's stories are generally terrible and few would be worth paying for.
The only one "with legs" I can think of is Drizzt's origin story, but it has a huge giant ohcrap problem with it, which I'm not going to go into here, but let's not pretend it's not a big problem.
People go to see LotR because it is highly promoted, by a well-regarded if somewhat minor director, it involves a well-recognised title, and when you see the trailer it looks beautiful and spectacular.
Yeah see the bolded bit. That's the thing. It's huge thing. It's not nothing. Minimizing it just makes your arguments seem hollow. LotR is a big deal, culturally, regularly appearing in "most important books"-type lists, or even WINNING most-loved book lists! Everyone who is even moderately culturally aware has some idea what it is.
I would be gobsmacked (but very happy) if any D&D movie compared to LotR. But it seems feasible that it could compare to Dragonheart, or even Ladyhawke.
Talk about aiming low. What movie studio would want to match the success of a poorly-regarded movie which made it's money back but didn't set the world on fire (Dragonheart), or a box-office-flop which became a cult movie? (Ladyhawke) That's insane. If that's what a D&D movie can expect (and perhaps it is - the D&D movie did about as well as Ladyhawke last time out, only critics regarded it worse and it didn't become a cult movie), any Hollywood exec will be having you escorted out of his waiting room, never to return.
Iron Man means different things to different people, too - to most people it means either nothing, or (say in the case of my partner) it means Robert Downey Jr in a funny rocket-powered suit. I don't think D&D is in any worse place than Transformers or Iron Man in terms of market recognition.
Transformers? Are you joking. D&D is so far behind Transformers, world-wide, that it's like comparing the Earth to the Sun. So that's just ridiculous. Iron Man is probably a good comparison, but the difference is, it's worth making an Iron Man film because the STORY has a great deal of potential (especially now). D&D has no "story", per se, and the novels and so have no particular cultural relevance. Most are actively irrelevant or hard-to-relate to.
I also don't know what you mean by "WotC lacking clear ownership of any world or character". They own bucketloads of them, starting with Driz'zt and FR, Dragonlance and all its protagonists and antagonists, then heaps of lesser-tier worlds after those one. (The Black Eagle Barony was mentioned upthread.) The D-Series - with its memorable characters including the giant rulers, Obmi, Eclavdra and Lolth is another example, rooted in the game itself rather than spinoff fiction. The Slavers, with memorable characters including Markess, the blind fighter in the eyeless helmet, and Stalman Klim leading the Slave Lords, is another example along those lines.
None of that stuff is worth paying for, or marketing, save maybe Drizzt and Dragonlance, and they both have big problems.
I'm not a marketing person, and so some of this "brand" stuff is a bit opaque to me. But wouldn't making "Forgotten Realms" or "Driz'zt" or (perhaps most plausibly) "Dragonlance" into successful brands count, from WotC's point of view, as a growing of the D&D brand? I don't see in what practical sense the novel line is its own product and brand. For instance, it's not as if someone else owns the rights and hence derives the revenue (is it?).
And even if the recognition on these D&D novels is not as big as LotR (but perhaps is as big as Iron Man?), they are still stories that could in principle be cinematised and thereby monetised more broadly.
You're not getting it. WotC doesn't have the money to force movies to be made, hell even Hasbro kind of doesn't. You need to make Hollywood WANT to make them. None of the D&D stuff has a good reason for Hollywood to make it. You seem, too, to be blindly assuming that movies are a profitable endeavor. Often they are not. You're not "monetizing" anything when your Dragonlance movie sinks without a trace after costing $150m+ (and it would cost that much.)
Who is justifying the multimedia thing being successful? At least for my part, I'm saying that it's not irrational, and there's no inherent reason why it couldn't work.
There are tons of inherent reasons, and the primary one is that WotC does not own any particularly appealing, relatable, "sexy" (in the broad sense, not the sexual sense) characters or stories for Hollywood to use. It really does not. D&D as a brand has little inherent value NOW, because that value has been squandered by years of neglect and association with low-quality products (the best of the recent D&D games has been mediocre, most have been dire, the films have been terrible, and so on - only the recent comics were above-average, and perhaps represent the best avenue).
So right now, there are tons of reasons.
But there is one potential hope. The mighty force of nostalgia, and the fact that "The D&D generation" is pretty much the one writing scripts and cheques right now in Hollywood and in the world in general.
If WotC can reboot the D&D brand, reboot it hardcore, and make it a brand that is associated with quality, exciting products, and they should probably start small with that, if they can get it out there, get people talking about it (and they have plenty of people in the media who seem keen to report on D&D), then maybe, three or four years from now, it would be a big enough thing that movie might be made, because of the name value or the like.
Not right now though.
So I just don't think your claim holds up against the evidence of the industry. Marvel Studios has not succeeded because of stories that were cultural touchstones before they were movies. They succeeded with stories about as strong as the stories of Drizzt Do'Urden and Elminster, Raistlin and Tasslehoff, Gord the Rogue, Mordenkainen and Bigby, etc..
They were a hell of a lot stronger and more accessible as stories than absolutely any of the characters you've mentioned there. It helps that they're based in what is essentially the real world, too.
Further, all of the essential stories there could as easily be told, reaching a larger audience more easily, outside of D&D, and without using the D&D IP or related IPs. Why bother with Drizzt when you could tell a better story with more cultural resonance and audience appeal by essentially having Rome be the Dark Elves and so on? Why pay WotC etc. for that story?
More importantly, even if you think the Marvel stories were more popular, I don't think the gap is as big as you think it is, or as important as you think it is. The name "Dungeons & Dragons" itself carries recognition for people, just as "Marvel Superhero" carries recognition. Those broad titles are far more important than the recognition people have for the specific character.
I have no idea, not even an inkling, as to
why you don't think the gap is big or important, and your post doesn't explain that. The gap is huge. Even the majority of the D&D players I know don't know or care who any of the mentioned characters but Drizzt and Elminster are (and perhaps Raistlin if you really pushed them), and more importantly, none of them would be like "Awesome, they're doing a Drizzt film!" or "Wow, finally a Dragonlance movie!". Rather they'd be doubtful, because the stories themselves are terrible and the characters unappealing. And that's actual D&D players, let alone the general audience. Whereas most superheroes are at least vaguely familiar to them, and most superhero movies at least elicit a "Oh, could be good!" reaction.
Four specific heroes (protagonist-human, plus supporting cast of elf, dwarf, and halfling) from a local village set out to destroy the evil dragon in the dark ruin of a lost glorious empire. Stick those characters in a Joseph Campbell plot arc, or a 3 act or 5 act structure, and you HAVE a movie. A million movies, really. All of which, with the right logo, anyone would recognize as a D&D movie.
Games and stories are conflict-driven. That conflict can be the same across media.
Missing the point entirely, I'm afraid.
You could do all that just as well OR BETTER
without paying WotC or using the D&D IP. Why would you pay? Normally it's because the stories and characters have cultural value/cachet or are intrinsically appealing (I know people like to pretend, for some reason, that LotR and Marvel characters have none, but's just not remotely true, and indeed, it's risible, all imo of course).
You're approaching it from the assumption of "I have all the money I need to make a D&D movie, what do I do?", and your suggestion makes some sense there (though it's a bit old-fashioned), but that's not the reality. The reality WotC faces is "I need to convince a movie studio that it is worth making a D&D movie specifically" (and likely WotC/Hasbro will want to get paid in that deal, making it less attractive to studios).