Are you sure the new instructor is resting his palm on the body of the bass? My take on the 'floating thumb' is that the whole hand is free to move, with the thumb muting lower strings and the fingers on the other hand muting higher strings. However, if your hand is still anchored in position by the palm, I don't see how it's going to be able to do the necessary dancing
I would explore this with your new tutor. Assuming that he can play in a way you respect, work with him to learn what he's doing - even if you reject his particular technique in the long run, it's unlikely to harm you. The most dangerous thing is falling into the trap of thinking that there's only one valid way of playing the instrument (although I'd be hesitant of approaches that are painful - no pain, less liklihood of long term damage

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Wulf