As a novice rider in the '60s it was de-rigueur to have ball-ended levers, as in front brake and clutch, they showed you were a serious rider, the straight-blade type levers were for mopeds, scooters and your mundane commuter-type motorcycle riders, not dare-devil Mike Hailwood wanna-bees like myself.
As a young child I took delight in my father showing me the white scar on his forearm where his clutch lever had pierced his arm during a spill on his Rudge Ulster. As the years have passed I began to wonder just when ball-ended levers were introduced. I can't seem to find a specific time, but it seems it was somewhere around early post WWII.
Here's an interesting article talking about all the complications of the clutter of handlebar levers for carburetor control, choke control, ignition timing control, clutch control, brake control and of course throttle control, and how it all developed and progressed.
https://www.classicbikeguide.com/control-issues/Speaking of twistgrips, I always like to have my throttle grip with a little resistance, enough where if I let go of the grip it would stay in that position and not snap shut. Twistgrips of my early era had an adjusting screw which pressed against a brass "slipper" which acted as a resister...............I miss that once-standard feature.