I can either take or leave a thumb push off feature,it does not effect the way that I withdraw from the pocket.
I grip with my middle and ring finger,push with the middle finger while grasping gun with ring finger and pinkie finger.
Thumb is along top of gun,and index is along slide as it should be above trigger guard.
The gun is pushed up out of holster with middle/ring fingers,and when it slides out,is gripped and taken out of pocket.
Sorry for the too much described sequence..
Having said all that,I do not use a thumb based take off,even though it may be on the holster.
I use a classic Hedley/Merlin front pocket.