Which purchased armor set is most op for utterly destroying enemies?

None. This game is incredibly easy once you get the majority of damage stats on the Skill Tree. Its horribly overtuned compared to gear thus making most stats on gear trivial, applying only maybe 10% of your damage output.

In the end, Speed is one of the strongest statistics and this can be effectively obtained on Mentor or St. George set.

If Attack were not capped at 30 points above a weapons base value, I would argue that Surtur sword and Sinner Skull would be decent weapons from Helix store but the fact that you can hit the Attack cap with just Mentor set and Adrenaline Fiend from the Skill Tree (or Adrenaline Fiend and 1 Diamond Rune for Attack) which makes all other gear with "Attack" perks null and void. It's a stupid design...or bug.

So don't waste your money on the store. Non Helix gear is just as good or better. If you want the best kit, Dual Spears is pretty much busted. Simple enough.

@bjgobbledix I agree, I have done the upgrades on my weapons/armors, because it's easy to just hold the square button down in PS4. I have hardly put any runes on any equipment because

a) it's a lot of steps to get them in the slots (ok, more than two)
b) reading the rune attributes is boring and they don't seem to do much

I haven't died in combat in a long time, except in Jutenheim, the strange beast surprised me and wiped me out quickly. But I came back and stomped him.

@thecosmicbob when I did a lot of testing of mechanics and turned off all skills (went back to Power Level 1), the game is definitely got a much more proper difficulty at that stage for Very Hard minus maybe enemies being sponges and you getting 1 shot by some attacks from Elites lol. The only part I hate is the fact I give up all the skills which I enjoy most of them. It's just the stats for damage and resistance.

But I do turn off Grit. This perk is just way too OP lol. With it off, at least I am forced to burn a ration or 2 from time to time. This perk just needs a rework. Straight up, would make it only function when below 50% HP with maybe a brief cooldown. Cuz then at least the "below 50% threshold" perks we have a bunch of can be utilized with much greater confidence.

@liquidblades the game is only challenging at the beginning, probably so people feel tempted to use the Helix store. After about 50% it gets increasingly trivial and even I ended up on the hardest setting, although I've never played any AC game above normal before.