There was discussion about this in the goalkeepers thread actually, and
@sifi36 has pointed out repeatedly (
example post) that United haven't actually lost a lot of points because of chances not taken. So it's definitely both true: United haven't really missed a lot of chances that were crucial to decide games; but if they had been more clinical, a lot of games would have been more relaxed (no nerves at the end of you're 3-0 instead of 1-0 up) and would have allowed for more rotation and experimentation.
@Adnan has argued that Ten Hag stepped into a bit of scouting void last summer: the scouting apparatus had justnbeen overhauled and apparently wasn't fully functional yet. You'd have to hope that's better now and less will rely this summer on Ten Hag's obviously relatively limited knowledge of the global player market.
As for Antony, if I remember correctly, he was pursued earlier (when he would have been a lot cheaper), but for some reason was only approved after the poor start - when he was also a lot more expensive and emptied the extra funds that were made available.
Obviously though, it's a lot of money for a player of Antony's level, and again a situation where you'd wish the scouting department had a bit more options prepared.