I am Dr. Jamie
This is a somewhat subjective question, but I will give you my personal opinion.
Ear cropping is PURELY cosmetic and unnecessary for any legitimate health reason. It requires general anesthesia which is a heal risk to the puppy and will cause some pain and discomfort for no good reason. So yes, I believe it is cruel.
That being said, the puppy will not feel anything during the surgery because they will be asleep. A good pain control plan should be used afterwards as well. An experienced veterinarian doing the procedure will lessen the risk of post operative complications.