1. Aquaman
2. Atrocitus
3. Batman
4. Captain Cold
5. Catwoman
6. Dr. Fate
7. Green Arrow
8. Harley Quinn
9. Scarecrow
10. Wonder Woman
That's not counting Deadshot, Poison Ivy, Red Hood, Superman, and probably Subzero but it's too early to tell.
Somehow the match up chart for Swamp Thing right now lists Flash as a good match up for him too, even though I don't agree with that.
I feel like Deadshot and Superman are 5-5, but others think they're bad, Poison Ivy I think it is in her favor but I don't know if it's agreed upon as a bad match up, most feel Red Hood is a losing match up but it's early so I'm giving it the benefit of the doubt and not saying it definitively, and Subzero's clone will probably act the same as Captain Cold's ice puddle that is the sole reason that is a bad match up.
So that's potentially 11-16 bad match ups, but my number is 12 as of now. His problem isn't just the top tiers. Nerfing the top tiers alone isn't going to help this character much since he has issues against all tiers.
If he's going to be a low tier character so be it, but he definitely needs tweaks from his current state.