Yes, I agree with all that, there are disadvantages to changing it. And it does seem like a reasonable belief to me: the perennial question WT has posed “a kingdom/government has rulers as well as subjects, doesn’t it?” seems fair, and the 144,000 a reasonable part of that “arrangement”, to use a theocratic word.
If they do make a change the reasoning could be as follows: the suggestion that some partakers are mistaken, or psychologically unbalanced, might have been conceived as a kind of stop-gap measure while numbers climbed temporarily. If numbers look like climbing indefinitely then that might be what motivates them to make a change.
As I understand it, the 1935 date was not arrived at from scripture, it was inferred because that’s when JWs themselves applied the Great Crowd to some of their own members in a novel way. Maybe the idea of the 144,000 not being literal could be conceived as a similar inference drawn from events within the modern day organisation.
Having said that, I agree with you the literal 144,000 teaching makes sense and doesn’t really need to be changed. But then, not all their changes make sense in my opinion. I don’t see the rationale for not counting time any more for example. It seems like a needless change with only downsides. Although I suspect in that case they may possibly have legal reasons for the change they are not disclosing.