The pinch between venture and ace is definitely different. Think of it this way. Ace turns deep and feels carvy. Venture is more of a lean than a turn. So when you crank down a crook with all your body weight, the ace truck is way more contorted while grinding. Meanwhile the venture has a much milder angle.
For me, it feels like the ace is more parallel to the curb and venture is so sideways it’s damn near like a noseslide. So in that regard, the techniques do require slightly different body weight distributions for long grinds.
At first I thought it was BS too but after riding ace for a few years and now on my second set of 6.1s, I understand it. An easy way to see it, is just push your truck down as hard as you can to simulate the pinch. Doing this you can see how much more contorted the ace gets.
And to answer the question of falling out of crooked grinds? Neither truck is gonna stop you from doing this on long grinds (I say long because this is where the body weight distribution really matters). You can fall out on both trucks if your technique is slightly off. However I will say that popping out to forward in the middle of a curb/ledge is immensely easier on venture. Maybe it’s because it’s in a closer position to a nose slide?