ah yes, this lovely argument again
It's actually one of my favorites to have because both sides have pretty good points, to the point where i've flip-flopped before in a series where I typically have very strong and unshakeable opinions, but I think I'd place myself pretty firmly on the third version side. The THIRD VERSION side, though, not the "whatever the fuck Ultra and 2 were trying to do" side.
Not only does it make for much better replays of specific generations (ie without Platinum, Sinnoh would be irredeemable, but it's now hailed as one of the best)- instead of going "should I replay Sapphire or Ruby", you can just go "oh I'll replay Emerald and get the best experience that way without missing out on too much"- but it's far better for your wallet and video game preservation. With DLC, you're paying twice for the exact same thing with minor differences. With a third version, you're paying once for that exact same thing but you don't even have to have bought the arguably subpar base games to participate. Both practices allow and enable rushing out shitty base games and saving the good stuff for extra versions to profit, absolutely, but with DLC you're essentially getting what could/should be a free update for cash twice over- and now, with SV, for more cash than the base game was worth (if you want DLC for both your versions)- whereas with third versions you can just buy the third one and ignore the other two.
DLC is also reliant on internet. Sure, there are limited releases of the game with both the expansion and the base game, but the vast majority of copies in the wild will be released without the DLC and therefore require internet to download it to your system as opposed to just buying the fucking game and having it forever. It's the same reason i'm viciously against Day 1 patches and patch culture as a whole- release a finished game or don't release it at all, don't launch in a broken state and then "fix it later".
Preservation is also the one point in which Ultra/2 has an advantage over DLC, because at least I'm not going to be spending 30 internet bux for something that'll disappear with the e-shop or my system files. I'm just gonna have Ultra or 2 forever, and I'm gonna be happy.
Also, if you establish a pattern of "2 base games and a third version", I think it's a lot more consumer-friendly than "2 base games and then DLC", because that way parents can simply wait until the best version is out to buy for their kid. That way, not only is the best version of the game rewarded with more sales, but it also saves the parent from the trouble of accidentally buying the wrong version or their kid missing out on the cool stuff this "ultimate version" added.
DLC is also restricted by the fact that it can't change the base game too much at all. If the map design is shit, you can't go back and edit the trainers or the routes because that'd be overwriting the base game. If the Pokémon variety is shit, you can't mess with encounter tables because it'd get in the way of the base game. The DLC areas are added on to remedy this, of course, but what I'm saying is that third versions can improve the base game while
also adding onto it, whereas DLC is forever stuck to just piling more stuff on the table in an attempt to fix the broken leg.
I'll admit, DLC does have a lot going for it. It allows you to experience new content with your old save file without requiring a whole 'nother run through of the game that you might've disliked on first playthrough (without the hassle of trading your whole team over and obliterating the difficulty curve), it's far more convenient, it doesn't screw over the poor saps who bought the base game and it's often cheaper than a third version if you just buy the DLC for one game.
Personally, I don't care much about doing things with my first-game team, convenience is the least of my worries, and I appreciate having multiple copies for a game as opposed to being upset that I bought an "inferior version", so these are non-issues for me
personally, though they're extremely solid talking points and I can absolutely understand why they'd push someone else to prefer DLC to a third version.
At least, no matter which side you're on, we can all agree that 2 third versions is bullshit and Ultra is one of the scummiest moves Pokémon's pulled yet lol.