When Austin was at his peak in 98-99 you can count on one hand the number of PPV matches he lost clean, the only one I can think of off the top of my head was Summerslam 1999, and even that was only because he refused to drop the belt to Triple H at the exact same event.
That said, as the biggest, most popular and most profitable star in the company he was absolutely within his right to refuse working with Jarrett; the only person it would benefit would be Jarrett by virtue of being in a feud with someone far above him who had nothing to benefit from it. Nobody would ever believe Jarrett was on the same level as Austin, so Austin winning the feud would have done absolutely nothing for him
In WWF Jarrett was always and forever would be a mid-carder for life and the only time anyone gave a fukk about him was when he was smashing guitars on women every week. If Austin had a programme with Jarrett It would have been like when The Rock feuded with Billy Gunn only far more pointless, because a) Billy Gunn had main event potential, and b) it was his first proper singles push so they were trying shyt out. They fukked up putting him on the mic against one of the greatest talkers in the business who basically ended his entire singles career with one promo, then Edge did the same thing again two years later. Jarrett had singles push after singles push multiple times over multiple stints in the company and every single time it flopped. There’s a reason for that.