Volibear Ultimate: Thunder Claws

So, I started playing LoL about three months ago. A friend told me about and I started playing it. Now I am level 21 and I main Volibear. A friend of mines gifted it to me and I started using it a lot. The problem with Volibear is that its ultimate ability seems pretty useless. It isn't really game-changing. When it comes to the late-game, I build Volibear tanky and in team fights, he is very good at initiating, but I never find much use for Thunder Claws, which is basically a twelve second Static Shiv Passive. It's true that it gives more damage output in teamfights, but when it comes late-game, the ability is pretty "eh." Don't get me wrong, but Volibear is good with his other abilities. Rolling Thunder to lead the charge. Majestic Roar when the enemy is grouped up and Frenzy as a finishing move. I just want a change to Volibear's ultimate. Maybe rework it to be sort of like Vayne's Final Hour, where Volibear gets more attack. Maybe his Rolling Thunder can get a greater boost of speed and make it unable to be slowed because when I try to gank a champion like Teemo, I always step on his shrooms to get slowed and he retreats safely. This is my first post and I really hope that Riot Games sees this and makes a bit of a rework to Volibear's ultimate.