[jqpabc123]

The different CEXs would have to coordinate such price swinging.

No they wouldn't.

All they would have to do is "loan" tethers to their "whale" friends with the understanding that they will invest it in bitcoin and hold until they are told to sell. See article from wsj referenced below.

It's easy to time the market when you're manipulating the timing.

you'll be paying a lot to the arbitragers

Exchanges don't pay arbitragers anything. People who sell their crypto too cheap do.