It's also misleading. The pilot pulling back on the stick makes the wheel harder to turn. If he stopped doing that and helped turn the trim wheel they would have been able to adjust it.

All that video really shows is that if you do it wrong it doesn't work. Not all that shocking

One thing I don't understand is that if the trim is stuck in a position that pushes the plane down, shouldn't the high speed (and therefore strong air flow) help to put the trim back in a neutral position rather than making it more difficult?

Because of the nose up elevator..

Here's the explanation in one picture: [1]

Here's the article the picture came from: [2]

[1] https://3.bp.blogspot.com/-6c8hfXS8WO4/XKd93voscrI/AAAAAAAAF...

[2] https://www.satcom.guru/2019/04/stabilizer-trim-loads-and-ra...

Nope, it is a jackscrew, and the aerodynamic load makes moving difficult, regardless of the direction.

See https://www.satcom.guru/2018/11/stabilizer-trim.html

I wonder how the simulator decides to change the required torque on the trim wheels. I suppose it must be a full aerodynamic load model?