Lower or remove the high towers and the portal in the middle of the solo map Portal. (to prevent camping, just as you did in nest)
I agree with this so much!
This also gets me on to something else which I would like to suggest.
About the Grappling Hook bow + elytra.
If a person has these he can just endlessly fly around and it's just sooooo annoying and almost impossible to deal with.
I don't have a good idea to fix this, maybe disable elytras after using grappling hook bow?
Also, if people have a shield wand with the mentioned combo, it's even harder to deal with, because:
If you finally get them below the map, they use elytra -> shield wand -> charge up grappling hook bow and use it -> easy escape.