Well, you still didn’t mention your type of workload with sync writes.
AFAIK, SSD without PLP can cause (recent) data loss in case of power failure. And the whole idea of sync writes is to protect (recently) written data from unexpected failure. So, while your sync writes would become faster, they would be less “safe” (in the case of SSD without PLP).
I can be wrong – I’ve never used SLOG myself.