He's amazing and achieved amazing things for Spain in the Euros...I still wouldn't say he's a generational talent.
For me, only 4 players have fallen in that category (Messi, Maradona, R9, Pele (just going by the achievements he had as a teenager and how he achieved those))
Seems about right to have 4 of those in 60-70 odd years - as in actually generational.
I'd call those all-time great talents. But I know what you are saying - being an all-time great talent is essentially defining a generation.
I would define 'generational' (as cringe as the term sounds) as being one of the best players of your generation. The four you mentioned are in my opinion - as I say - all-time great talents. After all, you can be generational, but if it's a poor generation you won't be an all-time great. In saying that, it is eerily scary how true your point there is, in the sense that Pele, Maradona, R9 and Messi are all about 15-20 years between their dates of birth (other than Messi being only 11 years younger than R9). It's consistently been shown across generations that a new amazing all-time great will arrive every 15-20 years or so.
As for Yamal himself - I think he can be top 2-3 player in the world. Although I don't really see anyone in the world under 30 who is more talented than him, certainly not in attacking positions. Maybe he could be number one but a lot will depend on if Barca can find the same success as previously or not. Unfortunately it's a team sport and no matter how good you are individually, if your team-mates don't mesh well with you it will be hard to be at your best.
There's also the fact that there are kids 5-6 years younger than Yamal who will be the same generation, but are currently unknown. There might be an 11 year old out there who in future will be on Messi's level for all we know. Unlikely, but we just do not know.