I'm moderate. In WH, U2, MAG, I'd tend to come in the upper part of the table, topping it some games, being best player others, and getting mullered other times. I'm not capable of matching the uber players with their massive kill-streaks etc. I've been on both ends of hammerings.
They have access to skills and feats that lower players don't have. They can have body armour, shields, more powerful weapons, etc. So no, everybody doesn't have the same possibilities. If the games separated players of different rank then they wouldn't be imbalanced, but pretty much every game I've come across throws low level characters with limited options up against top-ranked characters with all the bells and whistles to be cannon fodder until they've ground their way up the ladder, although Uncharted isn't a huge culprit there.
The other issue is not factoring in skill level either. There are different skill levels of players, just like in sports, and no-one would dream of mixing them together. We don't throw countless regional football teams up against Man U to be destroyed week after week, but instead form leagues of similar ability teams. That way everyone gets a fair game.
We had a whole discussion on balancing MP games a while back, and I don't recall there being any answers, but I still uphold my right to complain about games not actually being fun because the developers make some odd choices that don't balance things well for the maximum enjoyment of everyone.
That's why I'd rather play a game with mates against bots, where I know it'll be fun, rather in PvP where I never know in a round if I'll be on the team that pens the others in and boringly overpowers them, or I'm on the team that gets penned in, or there's a couple of amazingly good players dominating the game and I can barely move without getting killed, or if I'll actually have a fun game where the teams are balanced and there's a good sense of competition.