I have to really think about this. I'm not sure it counts if 80% of what you play is a shooter. With how many thousands of hours I've put into shooters anyone would be good at them. But for other types of games, I'm pretty good at those too. I'd say the times I find a game not hard enough outweigh the times I find a game too hard.
I play a lot of shooters, and generally if shooting things makes them dead, I rip it apart. I played Serious Sam on Serious difficulty on the last level, the one that lasts almost a complete hour through THE valley of darkness fighting an endless river of bad guys, at the end of which is a relatively dangerous boss, and finished it all on the FIRST attempt without dying. Got an achievement for that. To be fair I've done the level a few times on other difficulties, I only did it once on the serious difficulty.
I thought Bioshock infinite on the hardest difficulty was still too easy, though mostly because enemies refused to ever charge you if you take cover in certain areas. Abusing that can kind of sedate it. The other Bioshocks I played on hard and still managed to keep max money, a F ton of ammos, and very rarely die.
In Team Fortress 2 I manage to regularly stomp everyone who isn't a hyper-elite competitive player
Games like Fallout 3/NV I can turn up the difficulty and utilize safe "granny" strats and almost never die. Basically for such types of RPGs or minecraft or Don't Starve or anything where you can control when and how you fight, if patience is something you have in large abundance you'll do well.
But I'm going to have to think about other games. Difficulty can vary wildly. I don't really play RTSs because the level of effort and practice needed to complete higher difficulties can be absurd. I still play the ancient Total Annihilation but the AI in that game is pretty pathetic and if you pause to issue commands often, you'll outmaneuver it easily.
I don't play fighting games. I hate most of them in fact. They take quite a bit of practice to get good at, and frankly they don't keep me interested enough to care. It's just 2 dudes just fighting eachother the whole time. Booooring. Needless to say the higher difficulties will thrash me.
I'm going to agree with what others are saying about whether a game interests you. If you don't think a game is any fun, you're not going to stick around to try and get good at it, though there's a fine line between a game being genuinely uninteresting and a game you don't want to play BECAUSE it stomps you making you rage and quit it.
Now that I look at my steam list, it seems I play 90% shooters these days.... I thought I was a bit more varied than that, but apparently not. Still, I've played more than my share of many types of games and I don't consider them to be huge problems usually.