This is exactly what I hear from people who have ran their own funds. In particular, the person who ran a HFT in the late 90s through the early 2010s said he ra

This is exactly what I hear from people who have ran their own funds. In particular, the person who ran a HFT in the late 90s through the early 2010s said he rarely used anything more complex than linear regression with at most two variables. The speed of doing computations also matter here, his fund was eventually squeezed out by bigger guys w/ more racks. I did hear from a person who ran a quant fund with longer holding times that they used models such as Kalman Filter, which require far more computation to estimate values than regression.