Corrin's rolls weren't anything special (4-16 intangability and FAF 30) same as 12 other characters like Mario, DK, Falco, and sure a roll spamming Cloud might be annoying for people who are bad at the game on For Glory, but so is Duck Hunt spamming the best roll in the game and throwing projectiles, and they haven't nerfed that. This really seems like a case of them wanting to nerf the characters a little bit more but not knowing where to so they decided to nerf their rolls.
When comparing frame data across different characters, it's important to remember the "context" of the data and how the data fits in with the character as a whole. There's a reason why dodge frame data isn't uniform throughout the entire cast.
Duck Hunt having the best dodges in the game fits the playstyle the dev team had in mind when developing DH, which was probably a campy trap based character that is hard to pin down, hence why it makes sense for DH's dodges to be so good.
Corrin, on the other hand, is designed around zoning and spacing people out but has trouble when somebody is able to get through her wall. Nerfing Corrin's dodges emphasizes this as it slightly punishes Corrin when she fails to properly zone and slightly rewards the opponent better when they are able to get in.
For Cloud, I'm guessing they just wanted to make it slightly harder for a Cloud to runaway when ledge camping with Limit Charge.
Regardless, my point is I don't think saying "x doesn't deserve this nerf on z because y has a better z" is a good argument, if that makes sense.