Argyle King
Legend
And, pray tell, what is that "default playstyle" ? It seems to me, on the contrary, that there are already many, many playstyles based on 5e, with many if not most of the discussions on these forums being around people having different playstyles.
I believe that D&D, while still fantasy, has evolved into its own genre.
You mention other threads. You're right that a lot of threads discuss differing "playstyles" but it depends what you mean by that.
Are there people who play D&D differently in terms of magic items being rewarded, whether or not a race can be wholly evil, and so-on? Sure, but all of that still takes place within the context of how D&D works overall.
There are also threads which discuss how to emulate fiction (such as Witcher, Conan, King Arthur...); which discuss how to do things like romantic Arthurian fantasy; discuss things like trying to run gritty sword & sorcery; and promoting breadth of play rather than focusing so much on 1-20 vertical advancement.
Is it impossible to do those things in D&D? Certainly not.
But is the current structure of D&D well-suited to those styles? I would argue no.
You can certainly make a character, a campaign, or a monster which is informed by those ideas, but there are core elements of how the game is built which clash with them.
In a similar way, back when I played/DMed 4th Edition; I found that "ze game will remain ze zame" was not true. Some of the worst D&D experiences I had were while trying to run an edition in a way it wasn't built to be run. Once I got a handle on how the game worked "under the hood," I did work to modify it to what I wanted it to do.
Likewise, I highly enjoy GURPS (which actually is a "modular system"). Even as a fan of the system, I acknowledge that running something like Super Heroes takes a bit more work because the game assumes a baseline which is grounded in reality. Yes, I can and have run games which deviated from that baseline, but doing so required gaining an understanding of what the game's 'default' mode was and then figuring out which options to turn on to get to the experience I wanted. (Thankfully, the Dungeon Fantasy boxed set and Douglas Cole's products have done most of that work for me if I want to emulate something like D&D.)
The difference between the 4E and GURPS examples versus my anecdotal experience with 5E is that I could more easily make deeper changes without breaking some core elements of the game. Even a simple example like the idea that magic items are allegedly optional in 5E doesn't quite work because monster design assumes having a way to overcome damage reduction -against creatures which already have bloated HP totals.
I think the 5E options are great for adding or subtracting options... or for tweaking things like how long a rest takes, but not always great for when you want options which change the play experience on a deeper level.
Thankfully, I'm blessed to have a good DM running my usual group, and they're both experienced enough and capable enough to sit down and tweak things on a deeper level. But I don't see it as being particularly easy.
A lot of things about D&D make sense in D&D and to a D&D-centric community.