Pay-To-Win is an issue so I understand why quad cannons are mediocre. But at the same time Cryptic could start implementing items and powers so they behave differently in PvP. Giving PvE'ers fun toys that actually feel more powerful yet maintaining balance in PvP.
Yeah, Cryptic are sort of "Damned if they do, and damned if they don't" on this issue. If they tune the cannons to be the most powerful in the game, then they get hit with the "Pay to Win" tag, and if they leave the premiere weapons obtainable through very rare drops (DHC [Dmg x3]) then everyone poo-poos the new guns and doesn't want to buy them.
Personally, I'm loving them on my new Captain. I don't care that I lost a DHC slot. The cathartic grin I get every time those suckers fire is worth it if I'm playing casual PVE, DSEs, exploration or regular missions. If I enjoy the game more while playing actual mission content then I don't really see the downside. I'm having more fun, and that's all that matters.
...In PVP, well sure, replace them with a DHC if you so choose, but I have no complaints. More so as my stipend paid for half of it.