An exchange on RTF of this nature, and you don't know who is listening, only brings the FISO profession into disrepute, a simple correction to the readback would have been perfectly sufficient.
I'm always afraid that a 'rebuke' of this nature, especially to someone about to depart (no matter how many hours they have) might 'prey' on their mind causing them to 'miss out' a vital action before takeoff so I would either save it until they return, or if not returning, ask them to phone after they land.
Heath Row: I would suggest you contact the senior FISO at your airfield (if there is one) and ask to visit and observe what goes on in the tower. It's probably not a lot of good complaining to the airport authority as often they have little knowledge of ATS procedures, and would tend to refer it to the FISOs anyway.