An RNG is not a bad thing, if the rest of the game is designed to compensate for it. In FPS, such random mechanics tends to make solo gameplay less dependent on skill, but rewards team effort, insofar as coordination can minimize such random chance affecting the outcome.
I can't speak for CS, not having experience there. But in Red Orchestra, where weapons are even more instakill, and there's even more randomness (with things such as artillery strikes, that have unpredictable patterns on terrain - you can be in a trench, and if you're unlucky, a shell can land inside and kill you), good team commander and squad leaders are absolutely necessary to win, and a team with better leadership will run circles around the one that doesn't, even if the latter has better players, for this exact reason.
All of them, really (that are video games). It's a single series.
I would say that the most recent incarnation is the most tactical - ironically, largely because it disposes with some of the first game's realism, and makes squad leaders into moving spawn points for the rest of the squad. This means that squad leaders need to balance staying alive (to provide better spawns) versus the need to keep advancing (to provide spawns closer to important objectives); and squad members, on the other hand, need to protect their leader even at great personal risk to themselves.
It also makes flanking and other maneuvers that much more worthwhile, because the payoff for having your entire squad spawn on you near a gap in the enemy's defense line (or, better yet, behind it) is immense, and can make for a very rapid takeover of the objective, or deny the enemy reinforcements and allow the gap to grow faster than the other team can plug it.
So the team that provides the best collective cover for their squad leaders' advance is more likely to win compared to the team that just goes for kills, even if the latter is noticeably better at the run-and-gun mechanics.
I can't speak for CS, not having experience there. But in Red Orchestra, where weapons are even more instakill, and there's even more randomness (with things such as artillery strikes, that have unpredictable patterns on terrain - you can be in a trench, and if you're unlucky, a shell can land inside and kill you), good team commander and squad leaders are absolutely necessary to win, and a team with better leadership will run circles around the one that doesn't, even if the latter has better players, for this exact reason.