On a P/E basis neither Meta nor Alphabet seem overvalued.
The question is do you think you can get 35 years of this level of earnings out of a company. If yes or more then it makes sense. But a whole hell of a lot can happen in 35 years.
So, yeah it’s sort of like using that logic. Not exact as a dollar 35 years from now isn’t now, but you get the gist.
But I agree with the general problem of auditing advertising and performance. I've tried advertising on FB and my metrics never showed half of the engagement that they claimed.