I wonder if the strength was to help pin down struggling prey. The small arms would then be designed for aerodynamics -- to not slow the T. rex down when runnin

I wonder if the strength was to help pin down struggling prey. The small arms would then be designed for aerodynamics -- to not slow the T. rex down when running toward its prey -- but also help out when capturing it. That would prevent them diminishing further over time and find that optimal length for both competing requirements.