That's a sure fire way to never succeed as a team. I thought by now everyone was past the dumb premier league proven thing? Thats the logic that led moyes to sign Fellaini instead of Thiago
Van de beek excelled in the champions league with Ajax. Comes from an academy that is always one of the best for developing brilliant players. Grealish had a good season don't get me wrong, and is a good player. He's not worth more than Van de Beek is, and is IMO less suited to our needs, and far less proven as a player overall (despite being older).
How i see him as a player is a complete midfielder. He can do it all, tackle, pass, dribble, score goals, create. Like a Muller (far less proven and not on that level of course), but one that can play in any of the 3 midfield positions (to varying levels, IMO best as the 8 or 10 but heard he's good as a 6 too), is very intelligent, very hard working and physically good all around to adapt quicker to the prem. And hes composed, which is one of the biggest things that the Ajax academy always teaches, composure and technique to get that football intelligence.