If you are accepting that a Viper winning a regatta whilst using the 104 handicap is also a win as an F16, then it should be ok to sail the European champs on a viper using the 104 rating against the rest of the f16 boats?
But one could also argue that if you are not prepared to play by the F16 rules then don't bother to turn up to a F16 organised event.
Equally if you are prepared to design and build a boat to the F16 box rule, advertise it as a F16 compliant boat on the manufacturers website, race it as a F16 in events such as the Singapore championships which you mentioned, sell it to customers as a F16 boat, then AHPC cannot complain if the F16 class extolls its winning capability on its forum.
In my view its time AHPC came off the fence and decided which class they are going to compete in, 104 or F16, it would certainly stop all this bickering that is going on.