Where he plays is hardly relevant. As for not better than Nainggolan and Modric - maybe but he is 23, they are 7-9 years older. And if he continues to develop like he has over the last 12-18 months, he will be better than Nainggolan at least.
If is a big word. The ultimate goal of club as big as United is winning a prestigious EPL and CL.
Some of us, may not like an instant process, but history only writes a winner is a fact.
Continuing with typical potential World Class here and there wont take us any further.
Martial, the next World Class Striker. Depay, the next World Class winger ala Robben, Lindeloff, the next World Class ball playing defender. Pogba, the next World Class Midfielder.
Look at them. Are they potentially good ? Yes. But are they now fulfil the potential ? Big no. Are they expensively valued by their potential ? Yes. But are they worth the value ? Big no.
And where they play is relevant. It will be a determining factor whether they can adjust in EPL. Like an example, Darmian at his peak in Torino, considered one of best back in Serie A, but when he came here, he is flop.
Balotelli was a wonderkid of Serie A, but in City, he is just a decent type of striker. I can mention you other names, Jovetic.
I dont argue about targeting potential player like SMS, but to be valued so high, without any actual achievement is crazy and if we actually buy that without any firm strategy of utilising what you called this potential aspects, just like waste of money.