TSMC is clearly the leader and AMDs best partner...
... but the combination of multiple available advanced foundry fabs, very capable mature nodes useful for many products, increasingly sophisticated automated design tools and "cut and paste" IP blocks that subs will already have ported to multiple processes make switching, swapping or considering other foundries for bidding purposes increasingly viable.
Nvidia seemed to do pretty well with their 30xx series chips on Samsung. I have heard nothing about that slowing the development of the 40XX series at TSMC.