If we look at the performance of the three teams I mentioned, they also have good results in the Serie A, Eredivisie and Turkish league competitions.
We remember last season Leverkusen was the strongest candidate but it turned out that Atalanta won the UEL title. And this is one example that the 3 teams in the top 3 have a big chance to win the title.
You're right, there are many other stronger candidates. Lazio, Galatasaray, Ajax, Frankfurt, Athletic Club, and Anderlecht more deserve to be the candidates of UEL champion. So far, these teams are in the top 6 of UEL table. They also got 0 defeat, they only got 1 draw. Even, Lazio always won the match, they have 100% win record until now. In Serie A, Lazio also performed very well.