I completed all four routes, ~450 hours if I'm not mistaken, so, in that sense, you can bet it's got a lot of repetitiveness and very mundane tasks that you can complete quickly to keep progressing. It's very easy (hard in the beginning of Maddening, but manageable later on), too. Furthermore, allowing everything to reach level 99 is silly because you're never going to reach such heights, and, as a result, it's not very balanced.
With those things in mind, though, it's an excellent time sink and especially so if you don't mind god modes or self-imposed challenges. I would also argue that the cast suffers compared to previous ones in the series because everyone allied to you (Byleth and his/her little ghost) is very sympathetic to you, but it's still very likeable and there are a few standouts. I liked farming a lot to make everyone OP. When you're finished, it's so satisfying seeing everyone blasting everything in no time.
With those things in mind, though, it's an excellent time sink and especially so if you don't mind god modes or self-imposed challenges. I would also argue that the cast suffers compared to previous ones in the series because everyone allied to you (Byleth and his/her little ghost) is very sympathetic to you, but it's still very likeable and there are a few standouts. I liked farming a lot to make everyone OP. When you're finished, it's so satisfying seeing everyone blasting everything in no time.