I feel it would help with the character and immersion of playing on the server to have passive skills unique to each element. It feels a bit disconnected sometimes and not so natural that you can only press and select your bending move. I think adding passive skills would differentiate the elements more and define their play style better. As a bonus, it also doesn’t seem too difficult to achieve.
They could be learnt the same way as the active bending moves, being unlocked at certain levels, depending on how useful they are. As some examples: you could have fire resistance / thorns effect for fire benders, something like a jump boost / feather falling for air benders, water walking / faster swim speed for water benders and natural armour / reduced knockback for earth benders.