Since leveling skills beyond 7 takes lots of stuff is there any units you must level and you shouldnt lwvel because of their scaling? How much bonus damage is enough to justify wasting materials in a single skill?
Honestly I think this is a case to case basis. No one has really compiled data for that and it all comes down to how much do you need the extra dmg/tankiness/utility/etc. You just gotta check their chara info pages and see for yourself . A tedious process but provides a lot of insight