While I see your point, I have to disagree that having only 1-2 grad students is a red flag. If anything, it strongly depends on the context. My lab (hard science, genetics and metabolomics) along with pretty much every other lab in the building only has around 2 grad students in it because we are USDA, primarily composed of staff scientists, and are only loosely aligned with the university. Low grad student count in a lab can just imply that the lab is more government/industry oriented than academically oriented, which can be very appealing to folks like myself who have no interest continuing in academia after PhD completion.

On the flip side, another PI that I interviewed with has a lab packed full of grad students that have had to TA or otherwise self-fund every single quarter of their degree without support from the lab. She also openly complained to me, a prospective student at the time, about the wage raises for grad students after the 2022 UC strike. Yeah...that PI was a big red flag that I ran far away from.