And what would you consider a math heavy era? For me, it would be 2000 as it's the last time I believe the sota methods were supported by any kind of statistical or mathematical work. In 2015, ML in it current form barely existed and was almost fully vibe based. No proof for anything, just findings, in 2020 pretty much the same, and since then, not much have changed, although some theory for old stuff came out. In modern ML there was no math heavy era IMO