I honestly don't have much of a problem with the Russian planes anymore. Either they've been nerfed or I've learned how to deal with them. If they do kill me, it's a fair kill and I made a mistake somewhere they took advantage of. Also after having played them myself, yeah, that cannon is powerful, but it's really not all that crazy. They are slightly more durable than they probably should be, but again, nothing that can't be dealt with by good play.
Yeah, low tier is a little rough for anyone but Russians. No idea about jets yet. But if you give these "underpowered" planes a chance and learn how to use them, they can be very effective. I managed to grind my way through the US section of the weekend achievements and used the F4U-d the whole time and did quite well with it. It's fragile, not great gun-wise, mediocre turning and speed, but it's got decent climb(for a non Bf-109) and is hard to beat in a dive. I stayed in the top 1/4 of the scores the entire time and while I was using a p-47 and f6f (and a couple of backup p-39s which didn't get pulled out that often).
Yeah, the F4U gets torn up quite easily by cannons, but that's true of most planes. Don't put yourself in a position to get shot at by cannons and don't be afraid of running from a fight, which is more than possible in this plane if you play it right. Several times I ran, leading a train of enemy fighters right through a swarm of allied fighters which took care of them for me. Biggest problems will be surprise attacks and Bf-109s.
Skill is key. Watch some videos, learn some tactics, play smart and no matter what plane you're in, you'll do decently because most people simply don't think.