This fact which I also have seen leads one to say that, there are not two ways but actually four ways( not to mention four angles- in this case tip angled towards lower strings of the headstock is assume throughout) although the usefulness of the two other ways (LE LE) and (TE TE) may only be for developmental purposes if not actual play.
I understand that perhaps LE(Dstrk) (as it is defined here) would be preferable for thumb protection but, that requires pronation(or at least moving towards it anyway) which for me seems to be a crutch(like and animal that turns over in defeat). Supination requires the thumb bending in(leading to TE on the DS) which leads to the turtles head on the US(I get the feeling of a counter clockwise motion), whereas the turtles head on DS(tail on the US), gives the feeling of clockwise movement(that is to say if the cycle is repeated enough times).
I am feeling this is the issue with pick holding as the pick is constantly shifting between one side (L or T) and the other (T or L) as it moves back and forth on or between strings regardless of the actual plane of the movement Flx, Ext, Dev rotation. Sometimes the index finger needs a little help from a friend(middle finger), but that to get’s complicated as the same issues apply now with two fingers instead of just one(thumb is a given of course). As I have said in another place the faster you go the less this is a factor since the transitions are so quick.
Many a slip between the cup and the lip.
You think that the with the bias of left to right communication that the convention would be the other way though trailing---------->leading, but I can accept that’s they way it’s done.