I'm very reluctant to say this but 5150 sounds a rather irresponsible cha with whom I hope never to fly.
First he advocates transmitting over another aircraft - appalling radio communication technique which may achieve nothing except an annoying squeal on the frequency.
Then the bit about just slowing down - CAP493 is right. I guess 5150 has never watched the results of such action. I did once. An ATR42 which had been instructed to fly a particular speed reduced dramatically. The following 737 caught up so fast we couldn't believe it. Only a quick thinking Tower controller and the Grace of God saved the day.
5150 - you deperately need to be chained to a radar sector for a few hours to see what goes on.