I can't accept m43 mount.

Both the 90-250 and the 300 come with straps, for the lens.
Maybe the E5 mount is too weak for those lenses.

I've tried to use the 90-250 with my em5 with grip. I would use it if it autofocussed better, it is tough for me to manual focus and support the weight at the same time.

150, 14-35 and the 50-200, I have no such issues. I think a E520 sized Micro43 mount camera with a MMF4 or whatever would be fine.
I use the panny adapter, and it is sturdy. The MMF3 did seem that solid when I saw it.