I seriously doubt, you get more synergy if you bring a T2 ship into a T5 battle, anyway.
If you use the T2 ship, you will be less effective, therefore earning less points with the ship. Your credit and loot rewards will stay T2. You also might lose a lot more games than win.
In the end, what seems to be an “exploit”, is just like too early expansion in strategy games: you hope, having more territory in the start will benefit you, but actually, you get thrown back in total, and need a lot more time to reach the same strength, as someone who expanded once his economy was stable enough to carry it.
Now if you can play T2 ships like a pro, and still do good points and help your team win, you can benefit from this maybe, but it is very likely, that you won’t.
I fully support T5 restrictions, like having full decks in T4&T5 because of capture gamemodes (3 for T4, everybody in T5 should have 4 slots), no benefits for people who use only one single ship in the scoring system, and only having T4&T5 loaded up; Next to tier restrictions however, I also see the benefit of a “full synergy” restriction: to bring a ship in any tier above it than +1, it has to be fully synergized. So you have to know what you are doing; this would allow people to equip a fully synergized T3 in T5 if they don’t have enough ships for a full deck, but won’t allow taking those ships into T5 battles to synergize them.
I think, especially the deck rule would single out a lot of players, who play T5, because they own exactly one T5 ship. Such a person should not be able to enter lategame PvP yet. It is horrible, that some players in T5 do not know basic things, which should be clear to any regular T3 player.