Interesting post!
During basic flight training I remember being distinctly taught that during any phase of flight where Thrust/Power is fixed one should have their hand off the Thrust levers as pitch is what needs to be varied to control speed.
In the bus, even if the thrust levers are not guarded, full and continued up stick will automatically trigger Alpha Floor. It is arguable that by guarding the thrust levers, a quicker response is available to recover from these situations as opposed to waiting for Alpha Floor to activate.
I would also think that in the unlikely event that your seat unlocked and rolled back during takeoff, the instinctive action would be to grab onto anything, including the thrust levers, to arrest the fall back.
I can see benefits and drawbacks to each method, but personally tend towards not guarding the thrust levers during climb and hands on again at around 5000ft / below MSA during descent.