GT PL's were pretty extreme. I don't remember GT trunks doing too much but I'm sure he took a few hits from these uber powerful monsters and wasn't immediately turned to dust. That alone should put him healthily above USSJ Trunks
Trunks should still be on par with Goten in GT, the latter (when possessed by Baby) being able to force Gohan to go SSJ, and Gohan was noted to have kept up his training
I don't think Baby ever enhanced their powers though, not like he did with Vegeta's, who had a pretty clear difference in appearance after Baby possessed him
Yeah, those Baby physically possessed(ie. Vegeta) definitely gained a massive boost in power. Those he just controlled(ie. Gohan/Goten/Trunks/Bulma/etc.) weren't really implied to have gained much(if any) of a boost, iirc.