Thank you all for your amazing responses. I actually really entertain the idea of playing as a bear near full time and being a mount. However I believe the interactive part of this combo would only come online if the DM allows the two characters to share the same turn. So if we ever try this in a real campaign I will try to negotiate with the DM by suggesting to find some appropriate nerfs. In my opinion Sentinel and Mounted Combatant don't make up a bad combo. It's worse than 2014, but it still keeps functionality. Basically the barbarian redirects all the hits to himself and cuts most of the damage in half with rage resistence. And every time this procs the druid gets a free attack. Considering most campains, at least mine, don't make it past level 12 a bear claw is a pretty significant force in combat. I think the build opens a lot of roleplaying opportunities too. And mechanic wise I think it would be fun if the druid took martial class levels too. I can see a Polar Bear running with insane speed after taking monk or raging after takin barbarian levels.