I have for several years had a 4K screen physically positioned and in settings arranged immediately and centrally above my laptop screen. My large screen 23.5" wide and is as high as its stand will allow, and the laptop sits beneath it and is 13.5" wide, so there's 5" on either side of the top screen where the pointer will not descend.
Prior to Sequoia, I have been able - as described variously above - to position my mouse to one or other of the 5" 'shoulders' of the upper screen and then slide the pointer downwards, with the result that the pointer stays on the upper screen, but the dock shifts to the top screen, above the menu bar of the built-in screen, so I could move up from the lower screen's menu bar onto the dock on the upper screen. This was on both my ARM and my Intel Mac.
Far from having 'never been possible', it has been very ergonomic - reducing the distance my pointer has to travel from the multiplicity of windows I have open across a large area, reducing the distraction from my focus of interest, improving my workflow, and has never resulted in my having to 'play whack-a-mole'. Most of us don't live on 512x342 pixel screens any more, so there are various other decisions made back then which are also probably due for a bit of different thinking - mix the dock into launchpad, context-sensitive application menu, etc.