I've heard legends about entire ETL processes being coded in Excel, but I haven't encountered them (yet).

I have, multiple times but in the same company so let’s count as one. VBA is still a thing in banking/insurance and big consulting players are still selling VBA projects and/or XLLs in this world

Small note: my company is a quant hedge fund, where all researchers are technical.

Nope, the company has < 300 employees in total and < 100 working in technology.