Honestly, these problems are not balancing issue as much as it is map/mode design problem.
I am playing mechwarrior online for too long to not notice pattern here. Nerfing support ships is not really good angle to that. In fact, it is good that dreadnought or destroyer can maintains defensive position when he is properly supported. This alone is awesome. Problem is, as you pointed out, game become boring, when it is just peak out, shoot, fly back fest. Maps are full of choke points yet these are very small and without any objective, if team will hold good defensive position while other ships will cover the flank, there is nothing what other team can do, without proper communication (and we know in PUG games, there will be never proper communication), so they can just adapt and keep doing the same.
If map will be static as are now, matches will become very boring very fast and what we call now just some boring matches, it will become meta and solo players, who want have some fun and action will die over and over and over again.
So what is the solution? I think it is to introduce dynamic or even asymmetric modes and maps. Where objectives can shift or there will be more objectives to fight for. Something where map control actually means something. I really hope they have better modes planned than just these two.
I was thinking since some of the ships have missile silos is to allow them to target an area properly instead of a ship, this mean an entrenched position will get showered with them but the missiles will cover more of the area and less concentrated on a single target so the damage is watered down. But this should have the effect of making the entrenched opponents rethink about staying in same position under fire.
To sum it up, allowing some sort of indirect fire saturation as a way to combat entrenched/camping opponents.