The first 2 Chasm albums aren’t easy listens and are definitely rough around the edges, but nowhere close to being bad. I get why they’re not as loved as the following albums though. I’d still take both over The Spell as a whole though. I’ve only recently purchased the newest one and haven’t listened to it that much so I can’t comment there.
Bolt Thrower is the definition of rock solid, but they’re undoubtedly less ambitious. They found a sucessful formula and ran with it. They’re easier to throw on if you just want some death fucking metal, I get that.
I haven’t listened to Malevolent Creation in forever. I remember the first two being solid and the rest being forgetable. They also seem out of place in a discussion with The Chasm, Bolt Thrower and Demilich.
Demilich rules obviously. But Nespithe is so alien, otherworldly and removed from most death metal it’s definitely not something I can just throw on whenever. They also only have one full length and a few short demos, so I’m
not sure why you brought them up in this light.
Anyway, back to the topic of Overkill. I’m only familiar with Feel the Fire and Horroscope and I like both. So this should inform me where to go next.