If you want to be a master spray and pray, running & jumping, 180 no scoping while in the air and strafing at the same time (which is a classic "satisfying" shooter like Quake, and probably has very little to do with actual realism or "realistic" gunplay), then invest into skill and you can do just that. If you don't want to fight enemies at all, you can skip these skills in favour of stealth or hacking. Sounds perfectly reasonable to me. You don't ask why you can't hit for shit with a sword if you have base strength and not even a fighter in isometric game, usually.
Unless you are one of "those" people who do not understand abstraction and RNG at all, and are bothered that with 95% chance to hit, they still miss in X-COM or even Fallout 1. BUT IS 95%!! My dude is standing right near him? How did I miss?? RPGS ARE STOOPID
Deus Ex made me feel good, because at first I was shit, but then I could hit anything while jumping from building to building, wrapped in some nanofield, deflecting bullets like I am in the Matrix. Same with Morrowind, which had shit combat, but if you developed character you could do similar stuff - jump with spells like ninja and murder everyone in one hit with enchanted daikatana. Heck, with a simple knowledge that you have to fight with high level of stamina, Morrowind combat is not even that terrible - people just did not bother to study what affects your chance to hit (stamina is the first thing; but a lot of others as well - your skill, enemy skills and stats, armor quality, spell effects, enemy stamina, etc.); Morrowind's reputation comes more from people who don't know how to hit in the beginning, because they did not invest into fighting skills and stats, and tried to hit crap at 0 stamina.
Anyway, it's growth, development, it changes your perception on your character and the game itself. That feeling of jankiness and weakness in the beginning is an important stepping stone to joy you get later. Also, it is a goddamn simulation. Your skill is 0, so you get 0 result. Most players are baffled by the concept of course, often regardless if game is 1st person or not (Avellone trying to kill 50 wolves with 5 strength and no combat skills), and I wouldn't bother explaining what is the point of all this to them.
that stuff has to come first, even if it dilutes the RPG-ness