The key difference is that in BJJ there is constant contact and you are able to use that contact, remain composed in a relatively safe position (although there is a lot going on and you are constantly making adjustments), and feel for the right opportunity to apply your technique. A standing fist fight doesn't happen like that at all.
As to the rest of your views on sensitivity, if you say it works for you, you must be quite special since many longtime teachers couldn't get it to work outside of chi-sau, but I'm not going to argue it with you.
Well I do not know about that, it is neither what I have heard nor felt myself. But I got to be honest with you, I would not rely on sensitivity against a good boxer. Fact is it is not something I would ever rely on as only tool, that is just begging to get hit. You need to have a good position, good structure, a clear path. Sensitivity is not gonna help you survive a punch or resist your opponent. It is gonna help you direct your hands in those cases where there is resistance, and I do not mean simply doing pak sau and then magically know what to do next from sensing.
I just train for more than sparring and fighting boxers. This is also why sensitivity is not where I currently train the most, not even close. But if I spend maybe 10% on that area that is something I consider quite a bit.
Just saying it does work in a fighting context, however it is not the same as saying it works for ALL fighting context. As I wrote, it is not the only tool to be used. It is just a tool like many others, one should not rely on a single sense.
Now I must ask you, you consider techniques like bong-sau and jum-sau and so on to be abstract movements to teach you punching only? There is no such movement in fighting? Given that contact and sensing is not part of your style. You have no ability to sense when your structure needs to shift, sort of like shifting a punch to bong-sau, prior to structural collapse?
So you are just strategically planning in advance how to react and hope that you see what happens around you in order to react properly? I seriously doubt you dont yourself actually feel what is happening and reacting to that sense when in close quarter.
EDIT AGAIN: I need to learn to write correctly so less edits. We dont just do chi-sau, nor do I feel chi-sau should be a prolonged game of having contact. It has a goal to find a good attack. If one can't be found that is because you are either not good enough and need to slow down or you are too good.
I think a curse of chi-sau is mastering it. When people master the chi-sau drill and have that as their focus the contact gets prolonged, it gets tougher and tougher to get the upper hand on your opponent and instead it just becomes a game of back and forth. Problem with that is that all beginners want to be like their sifus and start thinking that prolonged contact is the goal. Problem is that prolonged contact is a downside of them facing someone that is as good as them at keeping options locked down.
Well it is just a theory, there are probably many flaws with it and if offensive I am sorry, not intended to be offensive to anyone.