Ryu is a strong footsies character. The only characters he struggles against in this aspect are those with swords. If that's one of your main issues you could ask some other Ryu players for tips. Not trying to be patronising - just a suggestion. The other weaknesses you mentioned are fair game.
Greninja is currently 17th/13th (Top 16/Top 8 respectively) on
Das Koopa
's scoring project. He's a fair bit below the top 12 in terms of his scoring but ranks well in the next group of characters. He fares reasonably well in the current meta. People love to say "oh, but he hasn't done anything at a major" which isn't fair since his best players don't travel, nor are his best players on par with the best players of the characters above and around him (top 12 goes without saying and you have people like Ranai and Kame repping Villy and Mega Man).
His biggest issue is losing hard to Sheik, with less-than-ideal MUs against Cloud, Sonic, Diddy and IMO Rosalina. He doesn't really lose to anyone below the top 10 but a fair few of the top tiers give him trouble and there are plenty of even-ish high tier MUs he can lose.
The focus should be on labbing and improving his top tier MUs. The Sheik MU might be a lost cause though, and that alone means he won't be solo-ing any majors. Still, he's a fun character to use and should serve you well against all but the cream of the crop, where he's not useless but generally fighting uphill battles.