Silent_Buddha
Legend
FPS that I play would never be fine with just half a joy-con; its missing an entire look direction control stick, an entire Dpad which is typically weapon switches, an aim down sight button (left trigger), and most importantly a fire button (right trigger). its definitely incapable of playing a FPS without the means of aiming or firing.
If it's an arena shooter like Doom or Shadow Warrior, then ADS is irrelevant and often more of a hindrance than a help. The main loss is the use of the D-pad for quickly switching weapons or selecting items. While there is minor loss of functionality weapon switching can be accomplished via a button press, and item selection via the same button but held down instead of pressed.
D-pad and analog stick for moving and aiming/looking. Shoulder button for shooting. Buttons for jumping, weapon/item select, melee, and what else? Brain far at the moment. I guess a button for context sensitive actions.
It's definitely more old school but functions just fine for a shooter. You can't do more advanced things quickly (item selection would need to open up a wheel menu on button hold, for example), but you could still do them. But then again you really don't "need" item selection in a FPS/TPS unless its trying to be more strategic, and in that case it wouldn't hurt much to have item selection be more delayed than on a controller with more controls.
Regards,
SB