Who is he talking about here? It sounds like he's talking about headline stats like goals & assists, a defence of Grealish perhaps? With more advanced metrics the contribution of players can be quantified beyond those headline stats. Not everything of course but as time goes on all on it will be possible to quantify all on pitch contributions. What you're talking about with Donny can be captured even with the stats we have available to everyone today.
https://fbref.com/en/players/b0b4fd3e/scout/11160/Jack-Grealish-Scouting-Report
As you can see with Grealish he's in the top percentile for SCA
The two offensive actions directly leading to a shot, such as passes, dribbles and drawing fouls. Note: A single player can receive credit for multiple actions and the shot-taker can also receive credit
If Donny was being an effective 'link man' he would register highly on this metric.
https://fbref.com/en/players/50dc94ce/scout/10728/Donny-van-de-Beek-Scouting-Report
As we can see in his (limited) data set for this season he does score in the lower bracket of the high range for these stats. He's also in the 98th percentile for progressive passes received which also quantifies his contribution as a link man in attacking areas.
I think the question with Donny is that he's very much a 'system baby' and is he really good enough to have a system engineered around him at the top end of the Premier League?