Okay, strait up, these are badly designed, the reason why is that they encourage bad habits that get you and your team killed on higher difficulties.
Marksman focus: The problem with this is that standing still like that is a death sentence on heresy and damnnation, I know fatshark wants there to be a sniper playstyle, but without threat reduction, which is in the stealth tree, your just going to get yourself killed. It leaves you open for disablers, getting hit from behind in melee, snipers, and basicly just makes you a sitting duck. This keystone tbh needs to be fully scrapped and the devs need to come up with something else.
Focus Target; Okay this is actuly a good idea, mark a target and then it takes more damage from your tean. The porblem is that sense it relies on spending stacks, what WILL happen is that nobody will use thier target ping untill like a boss shows up, and thus the team is denied critcal info, and thus your more likley to die. If the stack spending was removed and replaced with a flat bonus on tag, that would mostly fix this.