They got stronger and weaker by a large margin within TFP. Look at season 1, where small groups of Vehicons occasionally held their own, somewhat, like in TMI, and Convoy. Heck, in Darkness Rising part 1, a pair of Vehicons went 2 on 2 with Bee and Arcee. As for the final battle, it didn't really remind me of the Rebellion battle. I recall that being pretty one sided, which wasn't the case here, with both OP and Scream being pretty evenly matched. Plus, Prime never did burning justice.