AMD and GloFlo split in 2009 but AMD wasn't able to start actually manufacturing their chips with other foundries until 2019 when GloFlo got downgraded to only providing the IO die for Zen 2. This is because AMD was contractually obligated to continue using GloFlo for that time as a condition of the split.

Zen 2 is also where Ryzen went from "exciting and competitive, but not top of the line" to actually giving Intel a run for their money in more than just highly multithreaded workloads.

Improved architecture put AMD within striking distance of Intel and the move to TSMC allowed them to pull ahead.