I can tell you my experiences here; I've played Zeton's Fox (great KS Fox main) and a few random Peaches (the name is escaping me, but there's a fairly decent IA one I've run into a few times). Fox is just terrifying when played at max speed. He has great mobility, and once he gets in, you had better guess right when he's firing off that utilt at which point he can just be super ambiguous with his offense, and it's pretty hard to avoid taking damage in general. Once you are at kill percentage, he doesn't really struggle to finish the job. Peach, on the other hand, has tons of tricks, but her mobility is kinda crummy so she's easier to keep away. She can pressure amazingly up close, but then again, so can Fox! Turnips are the key for her no doubt, but I'd really rather deal with turnip approaches than Fox's running speed. Then, when you get at high damage, just play safe and Peach struggles ridiculously to kill you. As G&W I easily survive to at least 160% every stock against Peach. It's just not hard; she just can't kill as long as you pay attention. Even if she pulls a bomb, just calm down and realize she can't use any of her normal attacks as long as she has it so you really only have to watch out for her throwing it or random Peach Bomber (which isn't very scary). Just play careful until she wastes it and then get back to normal play. To be completely honest and serious, the only characters I find have a harder time killing than Peach are Sonic and Samus. It's something she can deal with I guess, but it's still kinda crummy.
Her one big advantage over Fox as things stand is that Fox basically loses for free to Pikachu and has a really hard time with several other really dumb things. In general, I also don't think either of them have virtue in their movesets worthy of being that high on the tier list. It's not that they're bad, but they're just not good either. I definitely think much more highly of DK than both, though the abuse DK loses to is the most absolute of all and holds him back the most (I would probably rank DK #10 if DDD simply weren't in the game).
There is still seriously no reason this should be bothering you.