I think the argument isn’t that the DLC characters are so good that if you buy them it’s free wins. But rather, if you don’t buy them, you can’t lab the matchups in training mode. Knowing the MU, imo, is more important than how good a character is.
True, but does this really make DLC pay-to-win?
When that term gets used, it typically means the game lets you buy "wins", by purchasing something that grants a significant, indisputable advantage over players who don't buy it. The worst of the P2W games basically force you to buy-in, because the advantage is so great you generally can't win without it. That's definitely not true for most FGs (including MK11). As others have said, you don't
have to buy DLC to learn the MU; it just makes learning the MU easier. And you don't even need extensive MU knowledge to win against most opponents, as long as your fundamentals are strong.
Intent is also important. "P2W player" is almost always meant as an insult: someone who buys in-game advantages because either (1) they're too lazy or impatient to grind for them, or (2) they're more interested in winning than playing fairly. Definitely none of that is true for FGs. You can't grind for DLC even if you wanted to. And (other than a few rare exceptions) most DLC aren't broken and unfair; they're just additional characters for the roster.
For the most part, you buy DLC if you want to play with the character or just want to maximize your MU knowledge. If you choose
not to buy them, you're opting to live with a (small) disadvantage. That's your choice; it's not a dig on people who do buy the DLC or the game itself. That's a big difference imo, and why I'd never call FGs P2W.