So let me straighten things out here. Volibear's entire kit revolves around getting to a enemy and cc'ing them until he either kills them, or a teammate kills it. his Q doesn't stop him from being slowed, if he is hit by any CC heavier than a slow at all the q ends (Hello Alistar's W+Q?).
Also, if a Volibear is at the point he builds a Righteous Glory to catch any champion either; the opposing team has a lot of heavy CC and it is his only way to engage without being useless, or, he/she doesn't understand how to play Volibear, since Righteous Glory is barely a 3rd to 4th item on him and even then there are better items for him to use. If he is at the point where he has finished his 3rd - 4th item it's probably 30+ minutes into the match which makes sense that the volibear can 1v1 you since he probably has merc treds, spirit visage, and either Sunfirecap/Cinderhulk(enchantment). that will put him at roughly 2.2 to 2.5k health with 100's for both armor/mr.
The problem is not his kit, if anything he needs a few more buffs/balances to become relevant again in higher ELO. The problem is that people need to learn how he works so that you know how to disengage from him, or punish a bad engage. Volibear is an all-in style champion with his only escape is his passive procing and using flash + q to try and escape (which he is slower when not moving towards an enemy champ). If a Volibear is able to take you out, you either don't understand him in the first place or they are just good at Volibear.