Ole clearly doesn't think Fred and McTominay are better than Matic. That's why he relied on Matic after project restart. However, I think he learned from that experience that Matic can only be played so much until he's run into the ground. Its been like that since his first season with us under Mourinho: Started really well and gradually got worn down. I think if Ole thought he could play Matic week in week out he would. However, he probably feels that Matic just doesn't have that in the tank. So he's managing his minutes.
United would not be consistently linked with #6s across Europe unless the club scouts were actively hunting one. Ole knows the problem. He just also knows Matic can't start 40-50 games a season.