I don't get why people are viewing map simplicity so negatively

They just needed to adapt and fix it. In fact your complaints could apply to majority of the worlds. Look at omega sector.

Mass making linear maps for solely training purposes is dumb. Imagine the same map with a slightly different platform, much like spooky world with just different shadings/images/monsters. Dull fast.

Here's the thing though. I actually train at Omega Sector to stay away from idiots at jesters. Those maps are actually trainable and fine for training. I'm glad the Jungle portion can finally be used as an alternative training area. Do I wish the Crimson Wood mountains could also be again? Yes I do. Did I always think it was cool these massive maps? Yes of course I loved the map design of Masteria. But at the same time if you look at the rest of maple: Elin forest. It's all changing like that. We can't do anything about it so why complain? Why let maps bother you so much?(Not you directly). It just seems like over-reacting to me. I went in with high hopes of this being DECENT content and it was DECENT at best. I am not disappointed nor do I feel sad. If they wanted to reboot Masteria this could be a good start. We'll just have to see.