For a 210 manpower squad they would be good to cap the map faster or as response to some rushed out light vehicle. They're a bit inefficient in combat right for 28mp reinforce cost, granted their base stats are pretty good for an engineer squad. Wouldn't mind seeing it lowered to 26mp.
The only real nerf here is the fuel cost for UC really, and that's imo a much better solution to open up a window between the UC and AEC follow-up than increasing the build time of the AEC, as it doesn't nerf the faction as a whole. There's already compensation for it as T0 Sappers means you can repair the UC without burning munitions.
I don't know how even you can't see this as a healthy change overall.
Because I see it as a loss of map control due to IS bonus removal, further loss of map control and tech if you go for UC and while, as you've said, REs would keep UC high better then its self repair and maybe stay behind to cap while UC does its job, you'd need to be constantly aggressive with it anyway to compenasate for 1 IS squad less at that time, meaning less infantry presence. REs are indeed good, but I don't see them being appealing over 4 sections or 3 sections+uc and THEN REs(after tech anyway, MAYBE before with the change).
My point is, I do see the reasoning for a change, I just don't believe benefits outweight or even balance out downsides.
Yeah, it will open a new BO options, but it'll either be a dead BO possibility or osttruppen 2.0 resulting in REs being butchered in the following patch.