Generally speaking, I think it's a good idea that FAs are supposed to monitor and limit passengers' consumption of alcohol.
It also makes good sense from a PR perspective not to have any delays/flights/diversions caused by drunk pax (not to mention the cost).
But unfortunately you get the odd FA who is rather lazy / obnoxious and makes up their own rules.
I can't see how a regular pax would show any signs of intoxication after one beer and one G&T.