Well
110pgl, if you really have flown that much I am at a loss to know why you can't see something so obvious, or require it proving to your satisfaction.
Could you accept - with testing and study - it is shown that people grabbing bags at their feet does not slow the exiting of the plane? (And don't be surprised that with testing, other long held beliefs and procedures are discarded and new better ones are created.)
No because it clearly would slow things down. Perhaps you should write to the CAA because you don't appear to be convincing anyone on this thread.