Kayn's passive is one of the coolest designs in the game, but when it comes to playing around the passive, it falls incredibly short.
One of if not the biggest issue is that you have no idea what you have more of in games where the enemy team has a more even split of ranged /melee champions. You get a white progress bar with no indication of how much of each type you have. I used to think the tiny circle in the middle had a small blue or red tinge to it based on who was stronger at the time, but no, it's actually a mottled purple that never changes from game to game. This is HORRIBLE for clarity. What I suggest is a split in half circle with two bars that fill up independently of each other. One Blue, one red. Simple, easy to do, and doesn't take away from his theme at all.
The next issue, the algorithm that decides which form is unlocked makes no sense. I have played games where the enemy team had 3 melees and 2 ranged, and after doing nothing but smacking melees most of the game, I decide to edge out the last of my progress on the ADC and finally fill it out. I unlock Assassin Kayn first. What? How the hell am I getting assassin form when the majority of my points SHOULD be melee? This needs to be fixed like crazy. It's super frustrating to do everything you're supposed to to try and get the specific form you want only to somehow get locked out of it for the next 4 minutes. Speaking of....
THE LOCK OUT PERIOD IS BAD. This is the last issue I have with Kayn's passive. I understand that there's a reason why the other form is locked out. Kayn or Rhaas has gained enough spiritual fortitude to completely conquer Rhaast or Kayn. That makes sense thematically. But...why does that mean Rhaast or Kayn just give up on trying for the next 4 minutes? You know what would make this waiting period smoother? Let us ACTIVELY reduce it by hitting more melees or ranged champs. You can still collect melee or ranged orbs, but instead of making progress towards the bar now, they hasten the timer and give you access to the form you need sooner.
I seriously hope you consider doing any of these three things if not all of them.