That extends beyond pick players too, Geddy and Entwistle spring to mind.
I started with 2mm picks, using my guitarist brain that thicker picks give a more pleasing tone and I still think that for guitar this applies, at least to my ears. However, since then, I reduced the gauge I used until I was down to .73mm, not least due to Bobby Vega’s use of that gauge and using the rounder corner. Although it does add a sharper attack, it does make the bass punch through, whilst still retaining good low end. This might be desirable if you have a guitarist who insists on a low end heavy tone.* I still mess about with other gauges, but I don’t stray too far above the .73 (never lower), a Dunlop Jazz 3 being about as heavy as I’ll go. I was wondering what Chris Squire used, he being one of the more famous pick users and a Google search revealed a Herco Flex 75, which, despite the name, is apparently around the 1mm mark.
*I’d be inclined to put a sticker over his EQ section that says, “You already have a bass player.”