yes you can definitely grind honor levels without a sub. however in BFA most of the PvP mounts required level 40 to learn(not use), the AV event for instance had a revamped ram/wolf mount as a reward but 20s but it just sat in our bags bc we were high enough to learn it. Now with SL approaching i am not sure how the squish has affected PvP mounts so i cant speak to those but my guess is 20 will be high enough.