Brace from a wheel spoke to the floor of the car using a 2x4 and use an air powered impact wrench. It is unlikely that a helper can hold the wheel firmly enough. Make sure your hex driver is fully seated in the bolt hole. Tap it in there with a few light hammer blows.

With typical Benz engineering overdesign, the bolt has a tapered seat AND is also locktited in place. Once it is out the tapered seat is more than sufficient to keep it in place. The tapered seat offers a huge bearing surface.

By all means, replace the bolt if you can find one.