Yes, they are (with some exceptions) able to use normal rifles just fine, but the problem is that they aren’t introducing new things.
Like my Sister Reject idea is ill suited, I’ve known that since before launch, but not due to lore, nor due to the abilities, but the lack of exclusive weapons that it can introduce.
But it still could introduce new weapons, new abilities, and new exclusive and untapped cosmetics.
Creating a new archetype, to then just have it work with the same weapons that the current ones do is quite wasteful, and would just create cost for practically nothing.
I’d argue that a Xenos archetype (Probably an Eldar, to sate the Elf fans and finally throw a bone at Eldar players) is gameplay wise the best, introduce new weapons that are out of the Codexes that we’re using, new personalities that are fully outside the Imperium, new reaction to the way the Imperium work.
And Tech Adept is able to lightly tap into that, because they are in the lore a sub-faction, or vassal of the Imperium.
Now can an Admech personnel end up in the Penal System of the Imperium, yesn’t.
Take Tech Priest and higher, it’s an outright no, they’re pledged to the Omnissiah and are bound to its laws.
Take a Skitarii, it’s and outright no, they would be stripped for parts.
Take Tech Menials, Adepts, Serfs and Artisans, as well as Technica Guilders and their workers, and there you end up with personnels that are subservient to the Adeptus Mechanicus, think like them, and if they managed to rise in the rank, would join, and would be much more inclined and learned (so trusted) to use Admech weaponry, even with the drawback that come from them (Severe and painful augments, weapons causing as much harm to yourself as to the target…)
I don’t prefer Tech Adepts, I’m on the Sister side.
But I’m able to make a Tech Adept tree, as well as pick 13 new melee weapons (With possible lore pairings, 1 shield, and 11 ranged weapons (with some having possible pairings)
I’m not able to do that with a Ratling.