The XT diameter trick I think is a joke. I don’t see much point in using it when I can go up a size or two in XL to get the same diameter(and extra breaking strength) & have a line that handles 10x better. Big Game handles way better than XT IMHO as well. I don’t think I’ve found a line that handles worse than that stuff. It does live up to it’s tough name though, but that toughness comes with extra diameter & fluorocarbon like handling characteristics.
I don’t think anyone ever claimed mono & fluoro had the same sensitivity, just that the sensitivity of fluoro comes from what makes it sink, it’s density which transmits vibration much better than mono, not it’s “lower” stretch. To me the difference is about like the difference between lead & tungsten weights, you can still feel it with lead/mono, but it’s not as pronounced as it is with tung/fluoro & for contact baits that extra feel is very important. There’s still plenty of stretch when I set the hook on fluoro(I’ve been using Spiderwire, which has a rep for being a lower stretch fluoro), which is why I’ve started going to longer rods for contact techniques to give me more sweep on the hook set.
Of course this is all just my opinion based on what I’ve read & experienced, which is what everyone goes by. If you believe fluoro has lower stretch & it helps you stick fish, it does, since 99% of fishing is what’s going on in your head & if you believe it & think it makes a difference, it does.