The Dutchman was in the Swans team which lost 4-1 to City this week.
"Currently they are simply the best team you can come across and you know that it is great if you beat them," Van der Hoorn told the BBC.
"These are not the games for us to win, but you still try to do your best against such a top team."
"You see what he adds to Everton and that is what we miss. That we did not get relegated last season was largely due to him. His preseason was not great, so his first matches were not very good at Everton.
"He did not play games here and that frustrated him. It was not ideal for us either. You can now see that he comes into his game and that he slowly grows into a star player."