Your actual experience is that you thought you were preloading angular contact bearings, and you weren't. Because you don't know all sorts of stuff about bikes, like how the loads are too small to require the preloading that industrial uses call for.

What're you talking about? Bike cup and cone hubs, cup and cone bottom bracket, cup and cone pedal spindles, are ALL angular contact. My newer hollow spindle crank has an end cap that specifies the torque for preload, so it's also angular contact bearings.

If the preload makes no difference, then why were the bearing balls and cones spalling and scoring when I had no preload, then with new parts and preload, not at all, for over 5 years now, way longer than before? The bearing manufacturer technical instructions described exactly my failure modes before, and how to prevent, and it worked fabulously. When all else fails, follow the manufacturer instructions.

Hub with twin cartridge bearings? I don't know if angular contact and if takes any preload, I haven't worked on them yet.

The pro bike tech at the better LBS here, we were discussing preload; For me, hubs are easy to adjust for preload, because my current bike has nutted axles that don't compress the whole axle. WYSIWYG. For QR axles, I use spacers with the QR closed to adjust for perfect preload. The tech, he follows Shimano instructions for QR axles, snug down cone on the balls and then back off a certain number of degrees, then lock down; When on the bike and QR locked down, he says it'll have the proper preload. I still do preload "directly" because there's such a tiny rotation difference between perfect preload and too tight or too loose.

Hollowtech II BBs are not angular contact and you've been told that before. You aren't preloading the bearing with the tiny plastic cap, you are removing all the spindle play caused by the rubber seals.

Your "experience" with preload does not match that of any bike mechanic.