Exactly. Tifa wouldn't be the fighter she is if she didn't know how to keep her boobs under control.
You're absolutely right!
They had two options how Tifa could have been depicted in the game:
1) Realistic approach: We see a woman with above-average bust size, who has enough common sense how she needs to handle her clothes/outfit to be effective in martial arts.
2) Unrealistic approach: We ignore common sense a little bit, to insert fan-service, for letting her bust jumping around freely without support. The players who always choose Tifa in their battles as the main character will be "forced" to watch the bouncing of a busty woman's chest, in all fighting sequences (like in every Final Fantasy, battles will be the most pronounced feature in the game). It will translate automatically as an big aspect for the player, and therefore must to be mirrored in the ratings.
There is NOTHING WRONG to sexualise a character when that is the wish of the developers. NOBODY can get against that wish, so long it will be categorised accordingly in the ratings. When they still trying to implement contents that are not appropriate for their target audience, THEN the REAL Ethic Department will reprimand them. That's why they have an internal Rating Department (falsely labeled as ED), to avoid a scenario like that and to reach a general rating for all regions. The RD gives feedback for the contents they were asked to get advice for. The developers can still decide afterwards if they take the advice or not, because they still could contemplating about a different rating. There's no point in time where the developers are restricted on their decision making. Tifa's bust size was never topic at all in the first place, rather how a woman with her physique gets portrayed in her playstyle.
My opinion is they are trying to attain an TEEN/16+ rating for all regions. The second approach could be depicted as 'Sexual Themes' and that alone would get the highest rating in the US (DOA is an example). When they need to choose between this ONE aspect and their target audience, you can bet your G-Cups they will take the latter (btw is this my actual guess about Tifa's cup size in the Remake
).