I think the bigger issue is that idle thrust of a single Merlin engine (which is used to land the first stage) produces more force than gravity on the vehicle.

I think the bigger issue is that idle thrust of a single Merlin engine (which is used to land the first stage) produces more force than gravity on the vehicle. This means it can't "hover" so the final burn must be timed with exact precision to have ~zero velocity on impact. Doesn't give a lot of room for error.