A few points.
First, gauntlets were a battlefield accoutrement. You wouldn't wear them on the street, or to a social gathering. The samurai class wore their swords *everywhere."
Second, without a tsuba, the hands become an immediate and obvious target. Sliding down the opponent's blade disarms him or takes his fingers off, rather than trapping you against his guard. That alone makes a significant difference in strategy.
And finally, no matter how good your control is, accidents happen. They happen more often as you approach your personal limits, but if you never test those limits, it's difficult to expand them.
That's fine you say that so let's clarify.
Whenever real swords are mentioned you enter the field of battle so gauntlets were hand protection. In the field of battle gauntlets were hand protection and the tsuba was not.
How social gatherings or samurai class fit in I fail to see.
Real swords however is a side issue for it is obvious that if I say no tsuba then I am talking bokken for you can't get a real sword without one. (unless you want to be pedantic then you could find that there are 'some' real katana without them.)
On your second point of hands becoming a target well you say it as if that's bad. I would say that's good 'strategy.' I would also say that bokken sliding down bokken is the result of bad movement. So we differ there, thats fine.
Lastly on your final point I will say this. Doing things based on accidents happen to me is merely a reflection of current unbudolike society. It sounds so reasonable yet can be unknowingly detrimental. Using things to protect or even do a person loses how to do it them-self. Washing machine breaks down, person don't know what to do.
So that last point is actually the one I hoped some might look at without me having to explain in detail.
Basically dependancy. Depend on washing machine, it breaks, lost. Depend on tsuba, one day no tsuba, lost. Depend on sword, one day no sword, lost.
Only on seeing this will a person realize there's more to it than meets the eye. The highest form of sword is empty hands. No sword, no tsuba, no excuse.
By the way I would say the primary reason for the tsuba on a sword is for when it is used in battle or practice to thrust into something like a spear. In this case it would stop your hand slipping onto the blade.
Personally, and I emphasize personally, I would say I see no other reason for it. Also personally I would say that a person pushing themself to their limits includes the point I made on control rather than excuses losing it for losing it shows beyond their limits so those who boast of such things thinking it's something good I can but smile.