I feel the same way, to an extent.
Mushrooms are really easy to farm, so I don't think they should be worth a whole lot. Sure, they take a little bit longer to grow/spread, but yea, they should be worth no more than like 10 ot 15 xp more than wheat.
Mining, however, irks my chain. I have 1025 excavation and I have less than 350 mining. I have done probably 2 times as much mining as I have excavation. Sure, I could go grind some obsidian, but it almost isn't worth it with the right pick. That xp rate should definitely be a tad higher.
Fishing could use some xp gain increase too. Same with woodcutting. Both of them make me cry to do.