Neonchameleon
Legend
I hadn't said a thing about any particular 4e class? I had compared my experiences with 4e combat to earlier-e combat and found 4e combat to be overall a slightly more complex and fiddly experience than before, and gave a supporting point to illustrate why that may be the case for me, in the context of illustrating that different editions have been able to accommodate different levels of customization, while remaining overall quite customizable despite this.
And I gave a counter-example of something that's more fiddly than 4e has anywhere which you accepted. Defenders are fiddly tacticians. This I don't dispute. I do, however, dispute that they are all at the upper edge of the D&D fiddlyness stakes and gave a counter-example.
That's up to the individual group, I imagine. The system can be built in such a way that none of it is essential to play. For WotC's purposes, I don't imagine they'd stray far from the pen-and-paper heroic fantasy that is traditional for D&D, but there's no reason in my mind that they cannot allow for other tables to have their own interpretation of what "D&D" means to them, even if it becomes a space opera game about politics and intrigue played using a monopoly board and poker hands. That might not be my D&D or your D&D or Jeremy Crawford's D&D, or WotC's D&D, but there's little need to play gate-keeper to what that word could mean for every table out there, and lots of reasons not to.
I think your second sentence undercuts your first one here. If you see D&D as requiring a certain kind of HP rule, then HP in D&D are single-purpose only.
I see all D&D versions as having had hit points in which a second level PC can take a point blank shot from a crossbow and walk away even if it rolls (non-critical) maximum damage. I see this as incompatable with realism - to me realism is one of those things that needs to be applied consistently. If someone isn't realistic in their area of expertise (which includes taking a beating) then they aren't realistic.
I don't think HP in D&D are anything like a "major system," so I can see a lot of different ways to use it to accomplish a lot of different goals for a multitude of different tables who might never use HP in the cinematic way that you seem to feel it must be used in.
They are foundational to D&D combat and consistently behave this way across almost all editions. And there are multiple cinematic ways it can be used - indeed the 4e "Heroic comeback" hit point mechanics behave differently from the previous "Tougher than iron" versions. They can be used many ways up to and including wizards having forcefields (yes, I've done this). What they can't be used is "realistically".