He's worse under Amorim because he's completely ill-suited to Amorim's system. I'm not going to slate Amorim for refusing to alter his system to accommodate Hojlund, though, because the system that Hojlund would work well in is the same sort of system which saw us completely out of control in the vast majority of our matches under Ten Hag.
Hojlund is honestly a pretty one-dimensional striker at the moment. As his goal against Leicester showed, he's actually quite good when the ball is played in behind an opposition defence. He's very quick for his size, and he's a good finisher one-on-one. The issue is, these sorts of chances will only come about frequently in a side that transitions from back-to-front quickly. Ten Hag's United did that but it came at the gigantic cost of ceding control of about 90% of the matches we played in, and hoping we'd have the quality when we did attack to negate that.
I agree that Hojlund was a better player under Ten Hag than he is under Amorim, but I cannot really blame Amorim for this because he should not understand any circumstances be making the same mistake Ten Hag did and compromising our ability to control matches to accommodate forwards who could only play football one way. He needs to be given full licence to gut the forward line this summer, and sign attackers capable of scoring goals within a slower and more controlled setup. We're never going to progress as a team if we always just revert back to fast transition football to accommodate attackers who can only thrive in that setting.