So buy it at a later date when all the content is available. A live service game is never complete at launch and if content complete is important to you, then wait until they're done with new game content and buy it when it's finished.
Im not quite sure what part of my argument appears to be going over your head, but you seem to be arguing a point that im not making. Im not complaining about how the game wont be content complete at launch - this is a live-service game, and that comes with the territory. My issue stems completely and entirely from the fact that it looks like a major update to this game will not be available - and will likely never be available - to people who decide to buy the game on Xbox One/Series X, or PC.
Again platform exclusive content is not new or unusual. Call of Duty, Nintendo, Tomb Raider, Soul Cailbur and many more have had platform exclusive content. Usually when content is exclusive it isn't that big of a deal. In the case of Soul Cailbur for example, that game had a completely different roster depending on the platform you got the game on. And nobody gave a shit. Tomb Raider had an exclusive PSVR mode because Microsoft doesn't care about innovation in gaming, this mode was then later ported to PC.
I see your point, but these are bad examples. The Tomb Raider VR mode literally cannot be on the Xbox, because it does not support VR. Not to mention that the VR section of the game, is literally just being able to explore the mansion, which is something that you can already do without VR. Whether or not you have this mode, is entirely inconsequential.
SoulCalibur's lineup changing between platforms is silly, but "Xbox gets Y, PlayStation gets Z" is not the same as "PlayStation gets Z, everybody else misses out", which is exactly what is happening here. Again, if this was something inconsequential, like an exclusive skin, I wouldn't give two shits, but this isn't inconsequential.
Most multiplatform games with console exclusive features tend to come in the form of timed exclusive features, like the recent CoD game's survival mode, or some exclusive weapons/armour in Destiny 1 & 2. If this was the same thing here, then it would be a bummer, but not too much of a problem - but it isn't.
Thus if you buy the game at launch, you'll get the same experience as everyone else at launch. So this post-launch DLC has zero effect on your release window experience
Again, I understand that the launch experience will be the same across the board, but this is a live-service game, so the game is a lot more than just how the game releases. After this Spider-Man DLC launches, one portion of the audience will get a drastic upgrade to their game and experience, that no one else will get. There will literally never be anything close to feature parity between the different platforms.
Do you not see how this is a problem, and a massive slap in the face to someone else who was looking at picking up the game on their platform of choice?