Envoy is a business (C) class product so they booked you in an equivalent class product. What's to complain about? They probably could have booked you in coach and gave you back the CP upgrade certificate if you really wanted but I would probably be happy with the Swiss C as that is a nice product.

Based on your situation I would not in fact complain but my tolerance for complaining about things is rather high. Since you got back to PHL the same day albeit 7 hours later that does not seem like the worst thing in the world to me. If you email a complaint you would probably get a small value travel voucher.