A motorcycle crash is a very violent event, there isn't any way to predict how you're going to come off the bike or how you're going to come to a stop on the road.
Four years ago, I got rear-ended by a truck. I was stopped, waiting to make a left turn, the truck hit me at ~40mph. I saw him just in time to get moving again, but my GS and I were thrown some 60' down the road. Witnesses say I looked a lot like a ragdoll in the tumble. I know my feet hit the ground many times, they were pretty bruised when I got my boots off. Would I have been injured more if I was wearing sneakers? Can't say, and I'm not willing to try it again to find out.
There are a couple advantages to wearing real MC boots:
Ankle and lower leg protection from hot exhaust and engine components.
No laces to hang up on the pegs.
A stiff sole improves comfort on the pegs by spreading out the contact area.
The soles are oil and gas resistant - if you step into a puddle of either, the sole won't start dissolving.
Many are waterproof, riding with cold and wet feet sucks.