Countersteering is convenient, but not required. A bicycle and rider are not a single rigid body. You can simply lean to one side and you'll have to steer in that direction to keep your bike under you -- no countersteer necessary.
I am not saying people don't countersteer, only that it isn't necessary to make a turn.
Also, bicycles aren't motorcycles where the weight ratio between rider and vehicle is swapped.
If you don't feel like clamping your handlebars so they only turn one direction, try this: coast along a straight line (and outdoor basketball court is great). Then pick a direction and just lean that way. You can absolutely keep your wheels on the line until you turn in the direction you picked, with no countersteering necessary.
This "fact" came about with a video of low skill riders who can't manipulate a bike very well, or don't know what it is they're doing when they do it.
He might be wrong, and just didn't know enough, but he is usually researching his videos very well and I would be surprised for him to be wrong about this.
What he demonstrated first of all is that you simply can't ride a bike that prevents the steer from turning in one direction. A bike continously falls to one side or the other, which gets corrected by steering in that direction to put the contact area back under the center of mass. This happens not necessarily through the rider's (conscious) action, even a bike with no rider does it to some extent, but in all cases it requires the ability to turn the wheel assembly freely around the steering axis.
IMO that means the bike in the video demonstrates failure to keep basic balance even before it gets a chance to demonstrate failure to turn properly.
just try it. roll perfectly straight and lean to a side. It accomplishes the same thing as countersteering, which is to put weight on one side of the bike, so when you turn that direction, the bike gets under you and you don't fall.
That's literally what they did in the video, I recommend you watch it. The issue is: you think you can just lean on the side you want, but you can't without counter-steering, so they devised a bike that literally does not allow counter-steering: you can't take a turn at all.
Because of the geometry of the front fork (rake and trail), if you lean to one side the bars will initially turn in the opposite direction. It's still countersteering. If you ever ride a bike where this geometry is wrong, which is difficult because it's so necessary, it's very different to ride, and you'll struggle to ride it non-handed.
I'm not sure your line method proves much since the countersteer could be very subtle. However I think you're still right. Countersteer makes you start to fall faster, but it clearly isn't necessary to make you fall because you do that anyway!
No it's not necessary in the strictest sense of the word, but counter steering achieves higher turn speeds, offers better control and precision, requires far less physical effort, and works at nearly every speed. I can't think of many pragmatic reasons not to use counter steering outside of just screwing around for fun.
I am not saying people don't countersteer, only that it isn't necessary to make a turn.
Also, bicycles aren't motorcycles where the weight ratio between rider and vehicle is swapped.
If you don't feel like clamping your handlebars so they only turn one direction, try this: coast along a straight line (and outdoor basketball court is great). Then pick a direction and just lean that way. You can absolutely keep your wheels on the line until you turn in the direction you picked, with no countersteering necessary.
This "fact" came about with a video of low skill riders who can't manipulate a bike very well, or don't know what it is they're doing when they do it.