I've had nothing but problems with UPS actually delivering stuff to my house, and the idea of driving to an industrial park to pick up a package at a shipping center is a joke. I've had no problems with the amazon couriers.
I assume this is on the back of the employees. And I support a model where I pay the true cost of delivering stuff, meaning appropriate pay for delivery workers.
But I think the writing is on the wall for UPS and other legacy carriers, and a strike is only going to accelerate that. They've already lost the goodwill of the public. Most won't even notice if the rest of their business goes to the Amazon focused couriers.
The problem is what it will do to the broader shipping networks. Presumably without ups, shipping will get even more expensive and have worse service for smaller businesses