I agree with all of this. I've long been a proponent of the Fighter and Rogue killing each other, taking each others's stuff, then being reincarnated as a Hero or Adventurer class.
Not going to happen, obviously, but unless/until it does, both classes will continue to struggle for relevance. Actually, there's a lot more than just that keeping them down. There's the 'gatekeeping' you mentioned, the 'everyone should have it' phenom that afflicts any non-supernatural class feature, and the deeply entrenched double-standard that's endemic to the community. I doubt that's even exhaustive.
I also agree that all of the archetypes in paragraph 3 are difficult to formulate mechanically and the tropes are often difficult to pull off in play (player-side). However, the 4e Warlord's suite of resources pulls all of those off in spades and the resolution mechanics certainly help eager, capable players who are up to the challenge.
Haven't yet seen anything help with the 'reluctant' hero, but the others, yeah, to varying degrees. Between re-skinning and some of the other innovations (I want to say 'mechanical innovations,' but really, fully exploring what the mechanics already implied is closer to the truth), you could pull off a surprising range things with the ruleset. The warlord, and giving more credit to/trying honestly to balance/whatever the martial source in general, seemed to be a big part of that, because it required re-thinking some things.
What's more, as you note in your final paragraph, the build is an enormous boon for GMs. I've used dozens of Princess/Lazy 'Lord archetypes as NPCs, Minions to be protected, or as Companion Characters (Heralds, Squires and the like) for players' mains. The prep is utterly minimal, the ease of use is a cinch, and the payoff is $$$
Nod. Of course, having done that in 4e it's easy enough to do with NPCs, by DM fiat, in 5e. For players, an actual class with solid mechanic is needed, and, really, DMs who aren't familiar with 4e could benefit from seeing a 5e Warlord in print (or better yet, in action, obviously) when it comes to designing or improvising such NPCs.