There is little doubt the security is overdone but one can kind of see why NATS did it. It would have taken just one person around the table to raise the possibility of vandalism and that would be the end of the argument.
The fact that the USA has had an online FP filing system, and the French via Olivia, and a few others around Europe, and none of these have been
openly and visibly vandalised, probably isn't going to hold much sway. If there have been nutters filing a load of flight plans for somebody's 747, the word has not got out publicly. One just doesn't know.
But the pulldown passphrase is certainly nonsense; this does not give any more security than any password entered conventionally. The extra security is just an illusion.
But one cannot compare Afpex with Olivia. Olivia works only for flights with one end in France. This is OK for many but is a dead end for many others who would have to maintain multiple logins, just to get around a bit of Europe. Afpex works worldwide - it is a direct AFTN interface.
Those who fly abroad only to France have lost nothing - they can use Olivia