Is backing up to time Capsule via WIFI as good as disconnecting the backup drive after each backup for protection against Ransomware?

Ransomware would initially infect the system drive of an unprotected computer. Most ransomware would be introduced, not by a hacker, but a user clicking on a link in a received document from the Internet. It wouldn't matter if that computer is connected to a network by wire or by wireless. Once infected, Time Machine backups to either a directly connected drive or to a Time Capsule, would theoretically become infected as well ... as the infected file(s) would be backed up since their file sizes would change.

So, neither backup method would be better than the other because you would never be fore-warned on when the Ransomware was present before the subsequent backup is made. Remember that as a minimum, Time Machine will attempt a backup once an hour.

Actually the backup on the Time Capsule is pretty safe.. regardless of the connection..

Recent ransomware attack used a weakness in ancient SMB protocol.. but that protocol is not used by the TC for backup.. it is still AFP even in the most recent MacOS.

And of course our Macs are pretty resistant to this kind of virus anyway.

But it is never a bad thing to have a secondary backup.. which you connect only when required.

Network backups do not stop ransomware on windows systems. So if they manage to get one into the Mac it is irrelevant whether you connect by ethernet or wireless.. you want to not be connected. Or to have strong permissions.. and this is now the case.. Sierra and High Sierra hugely increased protection.. which also made network backups a right royal pain in the rear.