Doesn't take much focus to swing a sword once or fire off a bunch of bolter shots. If Dante approaches during that, Eversor just uses the weapon in his other hand.
Eversor Assassins are in a constant state of inhuman rage and bloodlust due to the constant flow of drugs. They have to be put in cryostasis when not in use and only awakened for a mission because they're simply impossible to control or stop without outright killing them. I may be able to find some more direct stuff in a little while, but I don't see some random stun spell working too well.
Knockback shifts the range game in favor of the Eversor.
Dante may not be bad, but eversors are on another level. Even the weakest and newest ones would shred any non named non tier 6 Space Marine, and the best are downright ridiculous. One unnamed Eversor Assassin fought Liegenstrasse, the rouge Maeorus assassin, ending the battle in a mutual kill due to their bio meltdown. Liegenstrasse had previously defeated Darnath Lysander, a Culexus Grand master, a squad of hardened space marines who specialized in close combat, an Emperor's Champion, all this while dodging sniper fire from a squad of Scouts and a Vindicare Grand Master. Dodging Vindicare fire at all is an absurd feat as is, to say nothing of a Grand master. Liegenstrasse also killed the Culexus. Liegenstrasse also fought a squad of Terminators, Lysander again, a Librarian, another Emperor's Champion, the same Vindicare Grand master, and the Eversor Assassin. While the Eversor ultimately would be mortally wounded and secured the kill through the bio explosion combined with Lysander taking advantage of this, that nameless Eversor was the only one of any of those to be able to really fight Liegenstrasse on equal footing. Obviously this is a high end Eversor, but the fact that this guy wasn't even like an Eversor Grand Master or anything should tell you what types of monsters the Eversor temple cultivates.