I don't understand what you mean about "choosing to tie the whole of 5e to just one company"
What I mean is there are many games built on 5e now – complete core games. Level Up A5e has its own completely independent 5e compatible SRD. I'm using this one for the City of Arches. Tales of the Valiant is 5e. Level Up Advanced 5e is 5e.
FateForge is 5e. D&D has two different versions, both pretty different from one another, and both of them are 5e.
Again, 5e began as DYD 2014 whose core rules were put into the 5.1 SRD by WOTC. Absolutely.
But now 5e is something different. 5e has eclipsed WOTC and D&D and now it's the core platform for lots of RPGs and tons of supplements.
To use your car analogy. Saying 5e is just D&D is like saying your Honda Accord is really just a Ford Model T when it comes down to it. Really you're driving a Ford. Obviously that doesn't make sense.
You say you are making products for "all the 5es" but... not really? Your most recent project is the City of Arches, correct? And, as I understand that product it is mostly a setting and lore. I could use that product with Savage Worlds, or with a diceless system. Sure, the adventures might be harder to run that way, but you didn't design those adventures for Grimhollow, or for Ryoku's guide, or for Humblewood. You designed them to work fundamentally, with DnD 5e... which al of those things ALSO work with.
City of Arches is pretty system agnostic, true, but it's using 5e for a lot of it. I spent the morning working on a big table we're going to include in the back of the book that shows our bolded monsters and which variants you might want depending on which one of the four big 5e variants you might be playing: A5e, ToV, 2014 D&D, or 2024 D&D. Not all the names of all the monsters are the same so we clarify when a monster might have a different variant for one of those four systems. I'm guessing most GMs could figure this out but we figure we might as well help them out.
Also, A5e's SRD is awesome. It's like 5x bigger than the 5.1 SRD. Tons of awesome stuff in there, which is why we're using
that SRD instead of the 5.1 SRD.
when I sit down with people at the table, we are playing Dungeons and Dragons. If I backed your project and pitched a game to people, I wouldn't say "we are going to play Grimhollow in the City of Arches" I would say "I have some cool books for a DnD game, interested?" Because, at the core of this "platform" is Dungeons and Dragons.
I don't have a problem with groups saying "we're playing D&D" when they're actually playing Tales of the Valiant of A5e. I doubt Morrus cares. That's like saying we made a Xerox of something. I don't think my Wednesday A5e group would describe it as A5e to outsiders but we might start with "we play D&D. Actually it's a variant called Level Up Advanced 5e." and people would figure it out well enough.
The reason I bothered to write all of this is because I think there's a real value in seeing 5e as an open platform independent of any one game or publisher at this point the same way Powered by the Apocalypse is an independent RPG platform for everything from Avatar the Last Airbender to Thirsty Sword Lesbians. We don't say Thirsty Sword Lesbians is Apocalypse World just because they are both Powered by the Apocalypse.
5e is the same way. It used to mean "the 5th edition of Dungeons & Dragons" but now 5e means 5e. It's an open platform for RPGs.
You don't have to agree with me, of course. However, I think saying "5e = D&D" ignores the awesome work other publishers have done and are doing to build their own awesome and independent RPGs around 5e and I think it projects too much power over this awesome open slice of TTRPGs to just one brand and one company.