Quad Cannons are comparable DPS on up to Adv Fleet DHCs now. Many people remember a time from before this was true, so some of the advice against them comes from this era.
Are they "Best in Slot"? No of course not. You can squeeze out a little more with Anti-Protons and maybe even something like Phaser DHC MK12 [Acc]x3.
But the truth is, I use them on my Tac in Elite STFs every day, and in 9 out of 10 groups I am the highest DPS in the group. The extra that is available past what Quads put out is simply not necessary for eSTF optionals. NWS would be a different story but for me, I use this ship to grind dilithium.
As others have noted, if you're pre-VA (or might be on any alts), its the best ship in it's tier by far. Skin options are good too!
One of the better purchases I've ever made overall.