I think it depends. “You’re better off playing a game made for heists” is true if what you want to do is play a game about heists (or whatever). But as you say, you don’t really want to play a game about heists. You want to play a game that includes heists, among other things. Things for which a game made for heists may be ill-suited, or at least, less well-suited than D&D.
Sure, and this is why 3pp supplements can be so valuable. Because if I’m gonna play a game about heists as anything more than a limited run story, it’s gonna be either a fantasy heist game or a fantastical sci-fi heist game, and so if there is a 3pp book that adds heist genre mechanics and player options to D&D, I’ll just use that.
I think the core message is that system matters, and it is generally a good idea to pick a system that is well-suited to your purposes. Sometimes that means a bespoke system that was purpose-built to do exactly the thing you want (this is often especially true for one-shots). Sometimes it means a general system that handles most things well enough and can be added to as needed.
I think D&D’s biggest strength is in its recognition. Most people who play RPGs are familiar with it, so it’s very easy for most players to jump into, and they’re usually comfortable enough with it to be willing to push it to do things it wasn’t necessarily built to do, in ways they might not be comfortable doing with a less familiar system.
This dynamic is a big deal.
I do definitely hate it when people say "Just play X" This goes for both systems and classes/class combos when someone has an idea for a new class. DnD might not be have systems set up for a certain playstyle so you might need to create them yourself, but I do think it is still largely doable.
Same.
That said, I do think that there are systems out there which are better suited for certain styles of games because they have been built for it from the ground up. In this case they are much like DnD, they do their style of game well but a dungeon crawl probably not so well, and any changes to play style are largely going to have to be homebrewed because the system can't handle it natively.
I’ll disagree a bit here, because D&D is definitely not as narrow in focus as most bespoke genre games, or even some other general fantasy games. Most people I know hardly ever use a dungeon at all, for instance.
Im one foot into agreement on this and one foot out. I did quite a bit enjoy the Paizo adventure paths during the first edition run. They added a lot of mechanical elements such as kingdom building, romance, political intrigue, etc into the game. I think things that move the D&D needle off dungeon crawl and expand the experience are great. The results were very hit and miss, and often the mechanics made the elements hard to immerse oneself in, though I loved the effort.
Yeah, one reason I prefer to homebrew is that I can more easily adjust the mechanics I’ve added on the fly.
That said, I also am not a believer in universal or generic systems. I like using PF/D&D for fantasy, and Call of Cthulhu for horror, and Traveller for sci-fi. I like exploring systems beyond my wheel house. You can't knock it, until you rock it, I always say. Also, sometimes what im looking to run needs less weight than a D&D rule system offers. Sometimes though, re-flavored D&D just feels like D&D when you dont want that.
I think my group is lucky in that we don’t really experience
Space Fantasy! Feeling like D&D, or perhaps we do but in a good way? Like, it’s space D&D, but we are playing the kinds of characters we would play in Star Wars, and telling similar stories (kinda, the Galaxy is pretty different from Star Wars).
D&D is a bespoke genre game. It's just one you are really use to.
Nah. Fantasy is too broad to count for the genre part of that, and it doesn’t have any of the types of mechanics that directly reinforce a more specific fantasy genre tropes beyond some subclasses. If D&D is bespoke, every game that isn’t GURPS is.
Actually, there's a perfect example.
D&D does TERRIBLE at handling larger scale ... well... anything. Any time you have more than about 20 combatants, D&D just doesn't work worth a damn. It's horribly slow and boring. Don't believe me? Try giving your PC's a troop of about 20 men at arms, just bare bones Monster Manual Guards, vs a band of, say, 20 bandits and a Bandit Captain. Your PC's are, say, 3rd or 4th level. Just for S&G's, we'll say that everyone is mounted.
I'll see you in a couple of hours by the time you manage to resolve that. And those are as bare bones as you could possibly make them. No multi-attacks, no bonus actions, no reactions (except from the PC's and the Bandit Captain).
This is why ship combat is so difficult in D&D. When you have around 100 combatants, give or take, total, D&D, any edition, just totally breaks down.

I’ll let my group know that out mass combat and ship combat experiences didn’t happen!
I can generally run with an adventure arc within an ongoing campaign without needing to add rules. I'm not going to switch over to the Gumshoe system just so the D&D party can investigate a murder. Come to think of it, the AD&D module The Assassin's Knot was probably the first time I ever ran through a murder mystery in an RPG. But if I were going to play a game that revolved around solving mysteries then I'm more likely to use Gumshoe than I am D&D.
I feel that the D&D rules really lend themselves to adventures that involve heroic characters, copious amounts of violence, and the accumulation of an obscene amount of treasure.
The treasure part is purely genre convention and expectation, at this point. Not giving copious treasure doesn’t even involve houserules or homebrew.
And very often players have a D&D mindset because the rules push them in that direction which I don't think is appropriate for every game. So if I want to play a game where the typical D&D mindset would be inappropriate then I'm better off switching to another set of rules.
Not my experience, but fair enough.
I wasn't a fan of 4th edition but I didn't find it any more or less immersive than other editions of the game. I mean, we're talking about role playing games. I think it should be expected that the mechanics should support whatever gaming goals the author(s) have. Am I aware of the Hunger mechanics in Vampire 5th edition? Yeah. Just as much as I'm aware of needing a short rest in D&D. Neither one is particularly breaking immersion for me though. Although I don't mind being reminded that I'm playing a game not living a fantasy.
My original point wasn’t just about immersion. It was about mechanics that interrupt play, IME. Using mechanical resolution to determine my emotional state is just a play experience I don’t ever want, and I’ve never enjoyed in any of the games I’ve experienced it in.