Prototypical coupling speed is 4 scale mph or less. Few 3-rail locos made before the '80s would run for any distance at that speed, so gentle coupling wasn't a priority. I find that Postwar and early MPC couplers work pretty well at slightly higher speeds, say 6-8 mph. But in the '80s quality control waned, and that's when the trouble began.
Kadees definitely work better than modern-era O gauge "lobster claws." But the usual practice is to mount them on the BODY of the car (which may inhibit operation on sharp traditional curves.) You could make a couple "transition cars" to get yourself started. But if you want to perform realistic switching operations you'll have to convert your entire fleet, install appropriate magnets in the track, etc. -- a major undertaking.
Another option is try to fine-tune all of your O gauge couplers in an attempt to improve their operation. Depending on how much rolling stock you have, this could literally take many hours! As the number of manufacturers proliferated in the '80s and '90s, some of them strayed away from the time-honored Lionel geometry, or perhaps didn't exercise good quality control (K-Line and Weaver.) Their couplers won't mate automatically with other brands no matter how hard you press the two together. If you have some of these cars, you can swap trucks, or sell off the ones that are incompatible.
None of this addresses the epidemic of pull-aparts on long trains. Which brings us to the third solution, my solution: Keep the knuckles closed at all times. Black rubber bands, hair bands, twist ties, or zip ties are all discreet and won't hurt the resale value like crazy glue. When switching, back in slowly until the knuckles touch. Then lift the parked car up by hand and engage the closed knuckles over each other. 100% reliable, no slamming. If your sidings are out of reach, then you'll need to serve that industry with a specific set of cars that's known to be reliable. IMO among modern cars, the Lionels which have a tab that you push inward are about the best (but they're not convenient to operate by hand.)
Honestly, the whole situation stinks. I really think Lionel Postwar was better in this regard. Especially if you can live with slightly faster running and coupling speeds -- at least the product was equal to its promise. So much for progress! 
