You could absolutely make that argument. That is why this particular case is so interesting. This is the first time I've seen a ruling regarding this and it may open up for more cases on where to draw the line on when processing is "necessary" and not.

Also it's worth noting that GDPR also puts other demands in place, for example that there be technical measures to protect the data from unauthorized access, or unintentional data loss. If you can argue that a cloud provider can handle those things better, then that may trump the data minimization argument.

Its only a problem if its a company (and/or) using servers outside of the EU.