It might be 20 frames (I suspect it's probably more like 15), but what matters more is the 0 frames cooldown on hit. Also, it's an aerial, so you can drift in and out during the startup. The startup really doesn't significantly impact the viability of the move.
Awful for neutral is just jokes. Would you say Charizard Nair is also awful for neutral? Because it's basically the same move (except with lesser reward on hit and slower) and it's basically the entirety of Charizard's neutral play. And before you say "well, Charizard is an awful character and that's all he's got", it's equally true in PM where he's a much better character.
I can't help but notice that you don't actually own Smash 4 yet, so I'm wondering just what you're basing your analysis of this character on. There's nothing wrong with going based on high-level match videos (high-level players are better than most of us, after all), but what's been shown in videos just doesn't match your analysis of the character at all.
I would really suggest watching these three videos for a good overview of the character:
Oracle vs Denti (Sheik)
https://www.youtube.com/watch?v=QiFlpFNay0A
Oracle vs Bwett (Little Mac)
https://www.youtube.com/watch?v=A5_aUF82R6c
Oracle vs Jumpman (Mario)
https://www.youtube.com/watch?v=c9UZ-bzSJAY
You are, of course, welcome to post videos of good ROBs getting bodied at neutral by other characters, but even in matches where Oracle has lost you can always see the the character has good stuff. I really just can't see this character being less than Upper Mid with his well-balanced toolset.