Not it is not 'proven fact' that 'pot is stronger today'. You simply can't just say 'pot is stronger'. It's simply too generic. There's increased availability, increased production techniques, etc. It's not like pot magically got stronger. There's been potent weed available for thousands of years. What weed is stronger? Sativa? Indica? What strand of Indica? Who grew it? What generation is it?
It's no different than claiming alcohol is stronger. Where's the alcohol from? Who brewed it? What kind of alcohol is it? If I sampled beer 20 years ago, and then I sampled vodka today, of fucking course the 'alcohol' is stronger. Duh.
There's far too many kinds of pot to paint potency so generally. The entire idea of 'pot is more dangerous now' is 100% based in ignorance. If you understand how cannabis works, you won't say something so generic.
If I say 'fruit tastes terrible', isn't that a little too generic? Considering the wide variety of fruit available today, saying 'fruit tastes bad' means nothing.
So in short, no, it's not proven fact.