So each Merlin on every Falcon does a test fire at McGregor individually, then all together as a cluster when the stage is completed. That's two. Then, once on the pad, the stage does another test fire before launch, that's four by the time the booster is in the air and lets go of the second stage. Then, the booster performs a boost-back burn, regardless of whether it's landing on a drone ship or not (only the duration of the burn changes). Then it performs a reentry burn, then finally the landing burn. Notably, both the reentry burns and landing burns are done in a 1-3-1 sequence, with first the center engine firing then the center engine plus two outer engines for additional thrust then lastly the center engine again. That's a count of 7 burns for the center Merlin 1D, and an additional 5 burns over the course of every subsequent static fire test and mission.
On only a single Falcon 9 flight (obviously of those that are landing boosters) has there been no boost back burn. This was during the launch of the Bangabandhu satellite on May 11, 2018. Even if drone ship landings cut out the boost-back burn entirely rather than just reducing their duration, that would still only cut out one burn of seven. Your argument is literally nothing.