Many techniques work. I tend to roll my thumb downward because I shoot A LOT of revolver, especially cowboy action shooting and ICORE competition. CAS revolver shooting especially is strong-hand only shooting, as the weak hand is operating the gun. It's critical to have a rock steady strong-hand grip on the revolver as it moves from target to target. I've experimented with number of different grips and settled on that strong thumbs downward "fist." I specifically "set" the revolver grip before I start my run.
OTOH, I shoot a high thumb on safety strong hand with any single action semiauto and don't give it a second thought, and I've probably shot striker guns the same way, especially in competition.
There is never one "truth" in shooting. I've sorta had my nose rubbed in that point as I've focused more on precision rifle…my "technique" with the rifle, which worked just super deluxe with an AR under 100 yards, was a hindrance as I moved to longer ranges. "Absorb what is useful; discard what is not; add what is uniquely your own…"
Michael B