I think that's fair – it doesn't have to be read as some moral imperative (that's why I added the bit about it being potentially a piece of practical wisdom, I suppose).
But a few remarks either way – often people do slide from asserting a causal responsibility to a moral one (indeed in this thread it's happened quite a bit). Perhaps that's inevitable, but we can put that aside. We can question even the causal responsibility, regardless. E.g., the idea it's in your rational self-interest not to buy the game (/spend money on the game, etc), in the way you've put it, probably presupposes the idea that you are, in buying MTX/games, causally responsible to some degree for their continued success and their structure. (That's what you imply by the "baby step" idea of withholding spending.) But I just don't think even that point is true, really.
Unless you're spending hundreds-to-thousands, you're barely supporting this model and this franchise. Its success really trades on (as I understand it) exploiting the "whales" who do spend in such excess. I believe that's what drives this particular incarnation of the F2P model they've gone with (am I wrong about that?). So either you're not a whale, and so are not an impactful "consumer" for the company, or you are a whale, who does make such an impact. But even then, the archetypical whale lacks a relevant kind of agency to be considered even causally responsible: they act on whims and urges basically external to them, which means the causal chain starts with the manipulative behaviour of the industry. So, whale or not, gamers/consumers aren't really the cause of this model and its success – what is the cause is the array of techniques deployed by big publishers, and the surely many structural factors like governments failing to crack down on this exploitation or media failing to spotlight and critique it.
A larger ideological force probably pervades all these considerations too, and the attitudes of the ordinary gamer (or consumer of services and goods across many industries) are submerged in it: we are conditioned by a particular trend within the political economy to think there is no other way – what Mark Fisher called "capitalist realism". The reason so many gamers submit to the likes of EA, Konami, Activision Blizzard, Ubisoft, and so on – why people fork out for their entertainment products, or increasingly services – is that they just find themselves feeling helpless in the face of these behemoths. Gaming was a recreational or enthusiast hobby which provided some escape from the harshness of productive life, but it slowly got co-opted by a rapacious sort of capital that gradually squeezed the good-natured fun and aesthetic pleasure out of it. These forces are out of our control; we might convince ourselves that we can take baby steps by voting with our wallets, but really these kinds of non-protest serve to confirm our helplessness in the face of what feels like an impossible state of affairs.
We can of course look elsewhere, do other things, even in the space of gaming: turn to indie gaming; collaborate with others to create projects that serve our actual recreational gaming needs, or help to fund such collaborations. But such options don't seem viable in a climate of capitalist realism, even if they are, and this is another overarching factor that effectively disrupts our agency, making us barely even causally responsible for the successful gaming industry paradigms: we are acted upon, and our view of what is possible is restricted.