Waila itself doesn't need to be installed if the server has it, but this mod requires it. Fixing it would require something along the lines of setting acceptableRemoteVersions = "*" in @mod and potentially also making sure it's still compatible/detecting if versions are mismatched then.

Being able to remove Waila is quite important for some users to simply not see it, save bandwidth or work around issues.

Will be in the next version. Note also that this mod has no server-side functionality; the mod could simply be removed from the server to fix this in the meantime.

Will do. Thanks for reporting it.