So long as they're still getting infantry support from the planetary militia of whatever planet they're on, I don't think the reduced infantry component of the LCT itself is too much of a weakness. Otherwise, the LCT concept reminds me of the special tactics of the Ceti Hussars, which liked to break up their RCT into three equal portions centered around a 'mech battalion.
The FedSuns has so much border that breaking up their strength into smaller portions makes some sense. An LCT ought to be able to deter pirates fairly well. They can't scare off raids from other nations as easily, but everyone has internal issues to deal with, and that means they probably have some more breathing room.
So long as, over time, the AFFS slowly rebuilds the LCTs to their RCT sizes, viewing the LCT as a stop-gap measure, then I don't have any issues with it. Similarly, if they do keep LCT-sized units, then they'd better end up commissioning three times as many as they rebuild their power.