Fishing is ok but it makes the gameplay boring if it's the only thing that gives you better exp, or just rework for some baits by adding their passive not just their rarities, so that will make the baits even more useable (reference from fisch roblox), it's has really slow profit comparing to mining.
As for mining, since when I played the game that's the only thing I did and liked, especially it makes tons of profit even though it's slowly boring doing the same over and over.
And as for nether - it need a rework specially the monster alertness, the whole mechanic of them are really unfair in a small room/space.