Hi,
I haven't been able to replicate this issue in 8.3.8, so I was hoping to possibly get more detailed instructions as to what exactly you did? Or perhaps you should double-check this isn't an issue on your end (for example, you may not have refreshed external JSON files when updating from some previous version).
In my testing I used a level 100 Corviknight with +6 defence against a level 100 mew. Using
this damage calculator, the expected amount of damage in this scenario was 34.8 - 41.3%, wheras the move submission (which is an 80 power physical fighting move, but uses the attack stat) can deal 7.3 - 8.7%. Ingame, damage in the range of 35-40% was dealt, leading me to believe this is functioning as intended.