Again, I agree with most of what you're saying. Just a couple of things. Sure. But boxers have to rely on that hip pivot to generate that kind of power. We don't (but can add it in to hit harder still). It also means we can hit that hard more times within the same timeframe (obviously depending on training level). That's never the plan, but the whole reason I study kung fu is because it may not always be up to me. Not as true as you might think. I've gotten totally crushed by women half my size. At the last seminar I went to, I had a 60+-year-old man with both hips replaced go through me like I wasn't there. And I'm not a small guy (6'5", 240#). Nope. I will if I ever come across something that Ving Tsun doesn't have an answer for, but that hasn't happened yet. People train multiple martial arts because they (or their teacher, or his teacher, or someone) didn't master the first one. The doubt you speak of is indeed critical, and ever-present. power generated by boxing punches?
One. Don't fight people outside of a controlled environment.
Two, differences in size and reach are extremely difficult to overcome, no matter how skilled you are.
I'd continue to do Wing Chun and feel it was way past the time to pick something else to go along with it.