Ivysaur is an amazing character if you can space really well and know his strenghts and weaknesses. He's hard to learn, killing moves are hard to land and BS(bullet seed, not bullshit) does about 19% if you DI correctly. So BS isn't Ivysaur's best move. Also Bair spacing is pretty good. I think Ivysaur is a bit below average, maybe D/E tier but not F tier.
And I think Pit has the potential to become higher, but he's still not represented and with sagemoon quitting things aren't going to get any better. The Pit community sucks as well, only like 3 people make good posts on swf. He has potential, I'm pretty sure he'll move up sooner or later.