Well I have two AW Series 5 (wearing the LTE+GPS) both 6.2.8 and an iPhone 11 (also PB2) and when I go to the Activity app (after a 3.11 mile walk) they both show a total of 6,911 steps for the day and 3.4 mi. And they have been showing same numbers since I switched to PB2 and updated the two Watches (to 6.2.8 - didn't want to try WatchOS7)
I opted out of 7 too.
My mismatch started with DB2. To be honest, I didn't check DB1 for this.
Thx!