I don't agree that HAC is similar to the pulse laser. I would say every ship with a medium ballistic mount is happy use the HAC, but many ships with energy mounts struggle to use a pulse laser. The short range and high flux cost just cause the AI too many issues on many ships. Graviton is the only medium energy weapon that is useful generally (i.e. any ship can use it), but it has super low output so it's a waste to put it on ships where medium energy mounts are their primary firepower.
HAC is similar to Pulse Laser not by usefulness, but by design. Pulse Laser costs 10 OP, and not found at Open Market. Both appear to be the standard, unlike low-end Mining Blaster/Arbalest, or high-end Heavy Blaster/HVD/Heavy Needler.
I agree that Pulse Laser is not strong enough for those that can use it (Heavy Blaster is probably better), and too flux-hungry for the rest.
Heavy Autocannon is decent, but I do not use it very much for one among a variety of reasons: costs too much flux or OP (on smaller ships like Enforcer), less efficient than Railgun/Arbalest/Heavy Needler, range band does not match Heavy Mortar, too inaccurate, not as good as heavy needler. Still HAC gets the job done.
Re: Mining BlasterThere is one other ship I do not mind Mining Blaster on: Apogee during early game. Autopulse is too weak against enemy orbital stations. It takes too many hits for autopulse to crack armor. (Sustained DPS is comparable to medium weapon.) Mining Blaster will crack it faster. Good for playership Apogee attempting to solo an incomplete pirate orbital station early in the game. For early Apogee, I would sooner upgrade missiles to Locusts than mining blaster to anything less than plasma cannon (or maybe heavy blaster).
Still, Mining Blaster is too inefficient and costs too much OP for a junky low-end Open Market weapon.
Having a weapon that is literally only good on one ship is terrible design.
I have similar complaints with other weapons. Most of all, dumb-fire large missiles (in part because Hammer Barrage is low-end and Open Market common). The only good ship that can use them well is the Legion (XIV), which we cannot buy, build, or farm. Gryphon is a bad ship, and the rest cannot use them effectively due to conflict design. Next release, Radiant may be an option, but that is AI only.
Phase Lance is a runner-up. Anything I might want it on, I prefer another weapon. For example, AM Blasters instead of Phase Lances on Harbinger.