By watching them play? Just like how Ronaldo and Pennant were compared and it was very much clear how Ronaldo was superior talent.
You watch the players and make your own opinion.
You don't need a hindsight to see Ronaldo was one of the best talent in the world football. Terrible use of the word "hindsight" imo. That's nothing but a typical biased article with no question of benefit of hindsight
If you say Bebe will be a better footballer than Nani/Ronaldo then you will be rightly called out and no one will use hindsight argument.
Like I said, you watch and make up your mind. Not with some random stats, btw which I used last season to show Blind is more or less as good as Matic.
Then you missed most of the posts. Go and check his posts when Martial was signed then you will know.
There was direct comparison on cost, talent and everything.