The massive disparity in Master class acquisition time

Spoilers.

So I came back after not playing for a year and a half. World 6 is new to me. Neat, 3 new classes. DB, easy enough. Didn't have to unlock new maps. WW, super easy. AC? Oh, you haven't cleared the very depths of world 5 yet?!‽ You Need to have a billion kills to unlock 6 maps? Hahaha SUCKER. Hope you have lotsssss of candy

Just wild to me how extremely different one is from the other two. I'm sure I'm not the only person who pushed a strong character through W5 quickly to powerlevel the others. So two master classes are likely instantly unlocked and one might take days or weeks. Unfun