Although your concerns are valid, I'd rather wait and see the new forward gun change first. The main reason is that yes, the ship is big, but it's not as big as a Nomad gunboat and has a better shape than an Orca or a HF gunboat (other heavy gunboats). So it's not actually the easiest gunboat to kill in the game when it comes to groupfights, although admittedly all of the gunboats mentioned have something unique in return (cruiser turrets, special FG, very fast turn rate), so we're doing the same for the Bret GB. There were a ton of changes this patch, so bear with us.
Yes, the Scylla has bad arcs while shooting directly back. To compensate, it has almost perfect arcs anywhere else but straight back. As someone who fies the ship often, what you want to do is always be in a ~20-30 degree angle when shooting caps so you activate your other primaries and increase your dps. Same goes with bombers and turret steering in a spiral, you want to try and make your ship be at an angle compared to the approaching ship, like a bomber, so you can hit it harder.
As for the nerf part, it's very justified. The size doesn't match a heavy core and 4 heavy turrets, and it should be a medium cruiser, not your "all in moving destroyer". If it was as big as an Irra, then it'd make sense.
You mean apart from 21 secondary turrets which give the Liberty Carrier an edge over all other battleships against any other class but battleships themselves, provided they stay in range of the secondaries? Not to mention it has a heavy core which means tanking other battleships is also a possibility. The Liberty Carrier is very well balanced at the moment, if you wish to be more successful in battleship combat, I suggest you try out the Liberty Dreadnough.
Thresher is a ship that was considered garbage as soon as it was upscaled, and nobody ever gave it a chance. Turns out, the ship is actually surprisingly good. Just look at the comparison with a Typhoon, the second smallest cruiser in the game. The sizes are very similar, and this is the post-upscale version, so you can see why it was upscaled in the first place. It also has a normal armor and a very good turn rate. True, it lacks turrets, but no other medium cruiser is this small except maybe the Dragon one, and that one has 7 turrets. Overall the ship is pretty solid and I don't buy it when you say that it's "incapable of dodging fire", because then 90% of the cruisers in the game fall under that category as well. People just need to give it a chance instead of calling it trash for no valid reason.