Grundy has a huge issue breaking through armor; The only way to do it is with Grave Rot active and its very unreliable. They buffed Grave Rots damage in the final patch but it did nothing for it's reach so he will forever be weak to the universal Wall/Ground Bounce.
Grundy can't help but be jealous of characters like Batman, Bane, Black Adam, Flash, NIghtwing, and Superman who basically ignore armor by using their trait, while fearing the likes of Lex Luthor for his armored shenanigans.
They could have easily made Grave Rot have the same range as it's meter burn variant while making the EX version stay active after Grundy gets hit and he still wouldn't be a top tier character. Mostly because there is way to much throw immunity in this game and he lacks zoning which is something that only Bane can cope with.