E450Coupe

I have a 2020 E450 coupe, bought certified in June 2021. Currently has 18,900 miles. 19" wheels with 245/40/19 on the front and 275/35/19 tires on the back. Dealer stated they put new Pirelli Cinturato P7s (summer) run flats on the rear right before purchase. Have driven 7,650 miles - in comfort mode - non-aggressive city and highway (to work and back) - since purchase and the rear tires are bald. Found out at they were bald at the B service, as the ride felt fine and I had not noticed anything different. Dealer said uneven wear on the front tires and the front was out of alignment so they realigned. Stated rear was in alignment and there is pretty even balding. I brought my husband to the dealership and they put it up on the rack and besides balding across the board, you could see an ever-so-slight variation in tread on the rears so they are going to recheck alignment. This is my first Mercedes and I LOVE the car, but I'm concerned about having to spend almost 2K every 8 months to replace tires! The dealer called Pirelli and they were willing to credit $100 but I would need to put a new set of Pirelli's on the car....which I would rather not do. I have had sport sedans in the past and have driven them extremely aggressively but didn't run into this problem until about 11-15k miles. I've been so careful with my coupe because I want to drive it for years to come.
Anyone have this same problem? And if so, any recommendations on the tire replacement? I don't have room for a spare so run flats will be needed.
Thanks in advance!