Granted, this is now almost a decade now but I was trained with the HK P8 which, according to what I can find, has a trigger weight of 24N (SA) and 55N (DA)
This would be 2.4kg force or 5.6kg force needed for pulling the trigger.
But as you said, it would make sense that even this is easily overcome depending on how you pull the trigger and the thumbs would be stronger doing that, especially with both hands.