I didn't select my dragons to demonstrate 4e distinctiveness
At least you admit it.
5e is exactly as amenable to "inspired GMing" as 4e was.
Indeed, all games are. Nothing a game could do can really stop it. In fact, you could even say that 5e primes the pump a bit, /requiring/ some inspiration on the DM's side of the screen.
Here's a thing that I'm not sure you're appreciating: if it requires extensive knowledge
...like memorizing 80 page of spells (see below)...
detailed analysis, and careful building to understand why the thing is distinct, it's going to be lost on a huge swath of your audience.
Not so much with monsters, really. The DM needs to handle the monsters and make them interesting. Some may do that via deep system mastery, others by seat-of-the-pants improve, and many things in-between.
But, it doesn't hurt to put a little more into the monsters, especially a few 'extras' at the end of a block say. Could be nice to have. JMHO.
(I'm cool with opt-in complexity)
I think that's all the thread really calls for from 5e.
The issue is that with a list of spells, or a list of feats, you've got one list of abilities that's fairly universal across the entire game. And everybody's basically pulling from the same list.
Everyone doing many of the exact same things is an issue, sure. Not a big one, I don't think - they do them in different combinations, they're still differentiated. (As long as there aren't definite must-have spells, then everyone who has those does 'em a lot, and become defined by them.)
You play the game for a year, and you're going to have about 80% of the feats and spells more or less memorized.
Even better, they're all in the PHB.
In 5e, even with it's slow pace of releases, most of 'em are. There's that elemental supplement with a number of spells, and couple in SCAG. There'll be more, of course.
And, yeah, you can get a lot of stuff like that memorized after a bit. If you're new, of course, you obviously haven't, or if you've gone through the process for a few successive editions, you can get them confused (an affliction I like to call 'versionitis,' when I'm making light of my suffering).
The downside with memorizing much of what everyone can do is that, well, you know what some creature you have no logical reason to know things about can do, if I were overly concerned with immersion I might make more of that, but I'm just noting it.
That means it's not just on you as the DM to get every ability right. Your players can correct you, and help you out by reading the spell description.
That is the nicest spin on arguing over spell descriptions I've heard in a while. But that's what you're talking about.
Yes, long, ambiguous spell descriptions can lead to disagreements, debates, even arguments that can suck up game time and even become acrimonious.
I really don't feel like it's out of line to expect that, unless I'm citing references from the books or quoting others to reinforce my argument that I need to explicitly and repeatedly state that I'm relating my personal opinion.
That wasn't directed at your opinions about monsters, but at the old edition war saw about fighters casting spells.
Hazard of multi-quoting.
I did not find 4e's powers easy to parse....
And yes, when I have the spells in the PHB roughly memorized and that's one of the reason why I find that 5e is much easier. That's exactly the point I was making.
If you can be bothered to memorize 80 pages of spells, but not 5 pages of 'how to read a power,' sure, I can understand how you'd find a list of spells simpler to deal with than a few clearly laid out powers using the terminology from those 5 pages you didn't memorize. It's just a matter of sunk effort.
Furthermore, you don't have this situation where the powers of the PCs are completely distinct from those of the NPCs.
You say that like there's something wrong with PCs being distinctive.
I never liked the fact that what NPCs had access to was so stripped down compared to the PCs, while simultaneously several NPCs of player races had access to abilities that had no peer among the powers PCs had access to. I understand why that was -- it was impossible to do otherwise in 4e given the amount of crunch PCs had -- but it challenged my suspension of disbelief.
I always find it interesting what pushes that button and what doesn't. Every caster on earth using mostly the same spells, whether they're conduits for miracles from the gods or studious bookworms or have power in their blood or whatever? OK? An NPC caster having different spells than the party wizard? A problem? :shrug: Ultimately, of course, as DM's we can give monsters or NPCs whatever we want.
But, y'know, there /were/ any number of PC-race entries in the 4e MM that had the same racial ability as PCs of that race, and instances of NPCs of a 'class' using a selection of powers from that class (which, let's face it, any give PC only got a fraction of the available powers) - 4e also left the door open to creating NPCs using the PC rules if the DM felt it appropriate, though it cautioned against it for the reason you site (PCs are created in too much detail), if it were an issue, it was an option. What's more, I don't feel like 5e's gotten as far from that as either you or the OP were suggesting. 5e monster stat blocks /are/ quite different from PC character sheets because monsters need less detail and players need more options and distinctiveness, monsters' multi-attack is different from PCs' Extra Attack, monsters have all sorts of special abilities PCs do not, etc... spells stand out from that by being 'samey,' I suppose, but they're mostly just a short-cut, re-using the closest available system to model something that'd probably be a bit different if the game had the resources to model the monster closer to the 'fiction.'
I don't think the OP is wrong for wanting to go that extra mile.