Hey Sharklion, thanks for the questions. Honestly I have a great time addressing stuff like this and talking it through, you're right that its one of the best and most unique elements of tabletop design. Here's my take on these. I hope it helps you navigate your campaign <3
Swarms
During testing swarms were incredibly fast and difficult to make space around. We nerfed their movement slightly to better align with the sort of play you've identified there; a group of enemies collects around you, then triggers a big swarm, surrounds and blocks off egress and piles on damage. They're intended to have unexpected burst movement; throwing one big limb of itself out to cut off lines, fling themselves in direct stretches, then fill in the space around them when they arrive, but as you said, the ubiquity of Breaker counters them fairly strongly at range, and their lack of movement buffs means they maybe don't get to feel as dramatic and explosive as we'd like. I would suggest exploring miniboss pairings to better enhance their abilities, but I'd also consider a minor buff to swarms generally, granting them some small bonus to Movement that goes down as they get bigger, where 1-7 unit swarms get +3 Speed, 8-15 get +2, etc. I'll throw something up on the errata page when I get chance.
Blazing
It's just not meant to be a super swarm focused mechanic outside of turning very large swarms into danger zones for the GM, and to discourage the prior tactic you mentioned of creating death balls of unswarmed enemies to hound the players. You could say effective swarming is a blazing counter maybe.
Attractors
I would say balancing the "gravity" of the two sounds like the more interesting read but both are valid. Throw a third one in there for some three-body-problem physics and see how that plays out.
Sharur limit break
I would agree that RAW you should be getting rid of all the tiles, but this is probably an easy concession to make, taking away another player's toys feels bad. Maybe a tweak to the limit that lets them absorb attractors at-will by moving over them for a short span of time would be neat, then the two players can kinda feed each other. A buff to damage or pull-range per devoured attractor or something maybe.
Malakbel
I don't disagree here, they're supposed to be the Fast Armor but it can be annoying getting ahead of everyone and needing to wait. Esp when you include sprinting or the slower squads.
Provoke
I'd go with the 3D6 option here cause it's meaner.
Theletus
Most of Theleus's guys don't have AGNOSIA effects. I believe the author of that faction intended to write a faction-wide special Agnosia thing that used the system in a novel way but never quite wrapped it up, so several of their minibosses just lack the form change, which is a shame since their whole waking up-frozen thing fits very well. This is on my list of Big Fixes to cover in the future, our bad.
Language of Kings
I roll then use half, but I think a lot could be said for saying its half the max. This was actually intentionally left open depending on your taste for power level.
Harvester
Depends on when it happens, if the AGNOSIA triggers before their turn, they get two turns, if its after their turn, they gotta wait, if its during, I'd say they have to wait. Newly spawned units can, I believe, move and act on the same turn they spawn.
Hazards
So there's kind of two answers here; the Devolve hazard is the only explicitly named Map Hazard in the book. Initially we wanted every faction to have a unique one, but as our authors went on the "Hazards" ended up taking on different forms (See the big snake in MIXIS for example) and the functionality ended up pretty anemic. I mean't to pivot the Map Hazard function to a more PbTA GM Move style arbitrary narrative tool, but never wrote the expanded explanation, so it's a pretty unsatisfying element of the book. I would use it as such where you feel like it (A river overflows, a toxic gas cloud bubbles up from the surface, etc) until I can write up a whole bunch of them for a future expansiony thing.
Hey thanks so much for your kind words on the project and the opportunity to address and think some of this through. HELLPIERCERS is a living game to me, and even with the physicals out in the wild, I want to get in and mess with the guts and clean up some of this stuff as an ongoing project over the next year or so. I'm glad the vision shines through despite the frustrations, and I hope together we can keep refining this till it shimmers.
Much love
Nemesis