Michelle competed against Kostner and Ando. Kostner snuck in ahead of her in 2005 when Michelle was injured and held back by questionable scoring on the short program.
It was Kostner who was grossly underscored in the SP. She skated a beautiful short program with a triple-triple and should have won the short clearly, yet due to being a young skater with no name was placed 4th. Kostner was nowhere close to her prime in 2005, nor was Michelle. Kwan was only underscored in the SP compared to Slutskaya who did a sloppy performance and was still gifted 1st, but as Irina was clearly winning that event overall anyway it is moot. Ando was also nowhere near her prime around then. Pointless to even bring up, unless you want to note Kostner probably even more out of her prime than Kwan managed to win their only COP meeting at Worlds, which I doubt was your intent.
I also didnt say Kostner and Ando were better than Kwan, I said they were better skaters than anyone Kwan faced on a "regular" basis outside of Slutskaya. Ando is considered one of the top 5 jumpers in history, and Kostner is an outstanding all around skater with some of the best skating skills ever seen, although inconsistent. Ando is a 2 time World Champion and Kostner is a many time World medalist and former World Champion as well. Both competed at the top level Kim's whole career, and were competitive virtually the whole time.
I think Slute as a competitor (and with the Russian federation behind her all the way) was far superior to Asada.
Yes Slutskaya is so far superior to Asada that during the 15 month period that most regard her best ever skating she handily lost to a 15 year old Asada at the GP final.

An underaged senior Asada laid waste to Kwan's "rivals" you refer to, going 6-1 vs Arakawa, Slutskaya, and Cohen combined for the season, and her ghost laid over all of them at the Turin Olympics as the winner was always a bit asterixed by Asada's absence. Yet weeks after easily beating Slutskaya to win the GP final she proceeded to Junior Worlds to be crushed by an also 15 year old Yu Na Kim, who also could have picked up another Oly Gold had it not been for the stupid age rules which didnt exist in Kwan's time (and without which someone like Tara Lipinski would have never been heard of probably as her hips were already bust at 15).
Michelle in her time competed against three Olympic gold medalists, Lipinski, Arakawa and Hughes
Michelle was on the way out as late blooming Shizuka was on her way in. They were basically rivals at one event, the 2004 Worlds. The rest of their careers Shizuka didnt even coexist in Kwan's World. Tara was a 15 month phenom like I mentioned, and during that blip she almost always beat Kwan. As for Hughes, like I said many regard her as the worst Olympic Champion in history, it is a toss up between her and Annett Poetzsch. She is not revered as some great skater just because she won the Olympics, that is for sure.
And there was also Sasha Cohen who was always one fall away from beating her.
Sasha couldnt even win a World or Olympic Gold when Kwan was no longer a serious factor. Lots of hype which amounted to nothing. As I said she isnt someone Kim would be remotedly worried about facing when Kim would put 20 points (or more) on her per competition on jumps alone.
And Lu Chen, we can't forget her in 1996.
So like Shizuka she was a one event rival.