The fatboy is a complex topic as you can see here:
https://forum.faforever.com/topic/4865/the-problems-with-the-uef-part-8-the-fatboy?_=1696441679442
https://forum.faforever.com/topic/4807/talking-about-the-fatty
Only arguing that the build-while-moving gives access to more parashields isn't enough cuz my personal take:
It's a counter against sniperbots, why should you invest way more than 15k mass for like 8k mass in sniperbots killing your army?
Or the problem with airsnipes being way too valuable (see the linked posts for detailed answers).
I'm not saying the change doesn't favor the fatty, but it's nowhere near enough to say it's in a fine position right now. Also I have no idea what the other balance team members think about it so it could be a discussion lasting hours if everyone has something different in mind.
Another thing are the shield-SACUs. Since the SACUs are going to change quite a bit in the future, it can be that they will be an important factor to consider as well. So yeah, overall not easy to tell right now.