HSA is actually really powerful, it's just that any ship that could equip it and benefit from it with the price it has isn't designed for long-term combat, but mostly burst nonsense. And those that are about long combat, are usually long ranged, because they're glass cannons.
Sunder, Fury, Shrike, Wolf are too squishy to fight for periods of time long enough to make the HSA deal annoying damage. By the time they get in range, they need to have most of the enemy shields removed by just spamming everything at their disposal. Sabots, blasters, PCLs, ambs. Having 3 tactical lasers and a graviton pointed at enemy is a waste of time. Considering a ship like the Shrike needs all these op points. Also, ships that use energy weapons usually don't have that many op points, with few exceptions. Like the Paragon. If you equip them with all the weapons, you have space for like one interesting hullmod. And if you choose to make that one interesting hullmod high scatter array, you are screwed. You have options like hardened shields, unstable injector or whatever... And yet you choose a hullmod that is somewhat of a debuff in plenty of cases. Especially considering your ship is meant to be burst focused with beams only being functional as a long range support role with other things stacked on top.
HSA is functional on an Odyssey I think. With Tachyon Lances HSA being somewhat strong. It's also quite functional if you are piloting a Sunder yourself and using a Tachyon Lance with HSA. You can play around using other ships as cover. And dealing huge amounts of damage. Especially considering Energy Weapon Mastery rewards being at really close ranges. And stacks multiplicatively with HSA. A built in HSA, Energy Weapon Master, and a bunch of other stuff can make a Sunder be able to freaking turn off Enforcers in one burst. But the AI is just too stupid to handle that kind of behaviour or simply too squishy. And unable to utilise cover of other ships to play around that fact.
Coming back to the Phase Lance. Truth be told 0.8 is the standard shield of like midline ships. With the exception of Conquest or Sunder which are going to be firing at you from the other side of the engagement. Usually with a lot of kinetic weapons that are going to drain your shield extensively by the time you reach them. Sort of. However, most late game enemies have shield efficiency below that of 0.6, so using a phase lance against them still sort of doesn't pay off. But the point of phase lance isn't to pay off when shooting at shields. But to blow up tough armour or finish off wounded targets.
Another aspect you need to know is that plenty of ships in the game tend to spend less flux than they can vent. I mean... It's just kinda autofit nonsense. And default fit nonsense too... Though that is just a theory of mine. I just assume that happens, cause it's an overlooked aspect in some builds. So firing at them with a beam weapon is going to be not so efficient, as they won't be over-fluxed often.