Pierce in 1997 wasn't even close to her peak.
To borrow your reference from the peak Pierce thread who was closer to her peak in 1997, Pierce or Seles? Obvious answer is Pierce by a landslide, that was Seles's worst year of professional tennis until her final year in 2003 where she was 30, and both too old and injured for the game by then.
Secondly Pierce's peak is not dependent on an overall year or time frame, you obviously know that otherwise you wouldnt even dare try to argue peak Pierce is superior to all. It is dependent on her form in completely random and rare matches or tournaments, which can take place any year she is even in the top 10. I wouldnt say the 97 U.S Open and Pierce's match vs Seles was absolute peak Pierce, but it was a very good Pierce who wasnt a huge margin below her peak. If you will notice from watching the match Pierce was playing very well, and you will note Mary Carillo is raving about how well she is playing, yet she still got well beaten and thumped in the last 2 sets by a very fat and slumping Seles in one of her worst years ever. So any question who would win between them at their peak is not even worth discussing.
Lastly it could easily be argued 1997 is one of Pierce's best years. She made both a slam final and a WTA Championship (the biggest non slam event) final. In her career she has only made 8 of those, and 2 of them were this year alone, and this is one of only 2 years she made 2 or more of such major finals in the same year. She also won a tier 1 event, something she only did 4 years of her whole career (5 total tier 1 titles in her career), reached 5 finals of tier 2 caliber or higher, one of the only times she managed that. She reached atleast the round of 16 of every major event, one of only two years she managed that. The only years she could be argued to have had a better year than 1997 are:
1994- Yet that said she didnt even win a tournament that year.
1995- Yet that said she did poorly in almost all the major events after the Australian Open.
2000- Although did nothing and eventually got injured after Roland Garros.
Oddly enough 2005 on paper is her best year ever despite being age 30. 3 major finals (including the WTA Championships), only year ever with two tier 1 titles. Yet despite this she got destroyed in both her slam finals and never got higher than #5 in a weak disoriented year for womens tennis. So if are narrowing peak Pierce down to years as you seem to wish this was probably the all time peak Pierce, year end #5, loser of 3 major finals, and a 2 times slam final smackdowned in a bad year for the WTA. So yep Peak Pierce = peak GOAT.
As this topic isnt about peak Pierce I will not mention her again in this thread but thanks for that, this was alot of fun.