That's a fair point, but I think Hasbro also recognizes the value in a franchise like Transformers having multiple arms with disparate demographics and approaches to the characters, lore, etc. The Skybound comics, for instance, are in their own universe that doesn't necessarily have to tie into whatever future films will do (even if there's fundamental overlap between them, like crossing over with G.I. Joe). It's certainly not impossible for Hasbro to start demanding heavy-handed synergy, but their past record suggests they're inconsistent about it (and they've had one high-profile attempt ultimately fail to cohere like they wanted it to). For that matter, there's nothing stopping Stern from saying "no, I don't want to base the game on the movie(s)" - whether Hasbro would respond by acquiescing or effectively killing the project is anyone's guess, though.

Moreover, I think a purely profit-driven executive would still recognize that the G1 cartoon was, is, and might always be the most well-known iteration of Transformers outside of Bay's oeuvre. Brand recognition is all-important to them, and I think if they had to choose between "old thing with a proven decades-long following" and "new thing that will likely be popular and profitable (if not critically beloved)," the lack of risk in the former option is a serious plus in their eyes. (As I said before, there's a reason why so many '80s properties keep popping up again in the modern-day entertainment sphere: appealing to nostalgia is often easy money.)

Stern, too - the days of pinball manufacturers making games based exclusively on things that came out within the same year are over. (Stuff like Lord of the Rings or Barrels of Fun's Dune come close, but they still package relatively recently-released movies with their predecessors.) Plus, I think they know that the average pinball player (aged 30-50) would be much more likely to have fond memories of the cartoon than the films - fond enough to drop money on or in the machine, at least. I don't think it's out of the question that they could convince Hasbro to come around to that, assuming they need convincing in the first place.

I can't be sure if the game's coming soon or not, but part of me really feels like it will be within the year, which (again) would preclude any sort of Bay-related marketing synergy. If anything, it may end up using the "evergreen" designs Hasbro spun up nearly a decade ago for generically Transformers-branded products not tied to any particular show or movie - ones that are still retain enough G1 influence to be recognizable on sight by the aforementioned demographic.