Don’t just work on your clutch, work on your body positioning. At a full lock turn your should be able to have the bike almost perfectly upright with practice). Move your shoulders laterally in the direction of the turn, using your outside knee to hook yourself to the bike. If you feel like your shoulders are totally outside the bike and you’re only hanging on by one cheek, you’re probably only half as far leaned over as you think.
This moves your centre of gravity over enough to let the bike stay upright through the U-turn.
I was taught ( and it works for me ) to control your speed with a combination of clutch and rear brake (like you are doing) with more emphasis on subtle clutch control than rear brake usage. The rear brake isn’t going to make you fall at these speeds unless you stomp on it. The front brake however is an absolute no-no, keep your hand well away from the lever.
Keep your throttle constant, no need to blip, no need to roll on or off, that is what the clutch is for. But try using more revs. On the 250 (so WAY less torque than your beast) I keep at about 5000rpm (power band starts about 7000). I’m guessing on the Bandit that 3-4k would be about right.
The instructors emphasized that the engine should be making noise in low speed maneuvers. Low speed high control of a motorcycle is not a silent art. As you get better you’ll naturally start using less revs.
Hope this helps.
“The two seconds between ‘Oh S**!’ and the crash isn’t a lot of practice time.”