Someone convince me that focus target is worth taking

You just wrote down what feels bad about it. It feels unnatural. Swapping weapons to keep up the melee buff feels bad. You naturally swap when something needs shooting, and suddenly losing dodge/attack speed and dodge distance feels extremely jarring. This goes against the natural flow of switching weapons when the situation demands it.

If you go equip your ranged weapon with volley fire you don’t get the ranged buff, Crit rate boost only applies to the first shot.

I disagree. I actually like the psyker one, even the highlight one that points out that 2-3 last shooters that want to sneak up on you.