Let me help you out.
-Most players won't be able to use custom moves because they will be playing ranked/competitive matches, which would force preset variations.
-Those who play unranked/kasual matches will have to endure their opponent's augments, which will grossly upset balance.
-If you play with a friend (or manage to find someone) willing to disable augments, they will discover the meta as balanced as it was in the beta, which begs the question... why not allow them for competitive play?
-If on the microscopic chance a certain custom loadout is overpowered and it's plain as day to see so, balancing it is incredibly simple. There are lots of numbers to change about a move, from damage to whiff recovery to block adv. to even how many slots it takes to equip, or making it incompatible with other moves.