And where did you get the idea that Eversor Assassins make the best fighters?
In Ascension, for example (and I feel dirty for bringing this up), a Vindicare wins over an Eversor, period. And I'm not talking about "Bam, Headshot" kind of win. No, the Vindicare may as well get his trusty standard issue mono-knife and stab the Eversor to death, and statistically he's better prepared for it than the other way around.
Fluff-wise, the Vindicare is also trained to much higher standards, exactly because his profile necessitates him being an intelligent operative rather than a drug-crazed berserker, and much better equipped - Eversor's dreaded pistol is really nothing more than an Astartes-caliber bolt pistol strapped to a slightly better needler, whereas Exitus weapons fire friggin' intelligent bullets, Wanted-style. Clearly the allmighty Officio invests more in a Vindicare than it does in an Eversor.
Also, again, Vindicare training is pretty much the classical ninja training from 90's acion movies, starting with candidates killing each other en route to the training facility, and ending in unbelievably harsh punishments for the slightest failure. Even their personalities tend to epitomize the action heroes badassery - silent, focused, stoical, often possessed of a dry wit (pretty much a direct quote from the book here). In short, they're everything you want the Assassins to be, and they're already made playable in Dark Heresy.
But no, for some inscrutable reason, the Eversor must be the same thing, except with a pistol instead of a sniper rifle. Why? Because AlluminiumWolf thinks the Eversor Assassins are the coolest and most ninja.
Many design choices GW made over the years have made me cringe, but compared to your understanding of basic principles of game design, Matt Ward on his worst day looks like the lovechild of Gygax and Dostoyevski.
Do we need to go through characters in literature that would miserably fail a test of this nature but still manage to produce something compelling? You're reaching here.