Linux's market share in North America has breached 10% for the first time, says StatCounter
(www.xda-developers.com)
Statcounter doesn't have sophisticated bot detection like Cloudflare. Look at Cloudflare's stats for the same period and filter for "likely human". The percentage craters back to reality. So while I think "The loading times on headless alone would give them away." is total bullshit, they can still be detectable using other heuristics and an awful lot of machine learning.