"By all reports, ios sucks for this"
"across my 4k screen"
So, "by all reports", suggest you don't use iOS or an iPad, rendering your opinions less than totally useful.
"tiled across my 4K monitor", suggest you were using a big screen to show multiple windows. Probably More than 20 inches across diagonally, compared to the more normal 11 inches that iPads and other tablets use. In other words it's meaningless to compare work patterns between the two platforms. A multiple window OS is not desirable on smaller devices, especially when accessibility issues are taken into account.
They are different devices for different purposes. Previous attempts to make desktop OSes work on tablets and vice versa have failed. As a real-life iPad (and laptop) user I don't want any more convergence. Keeping it focused is not "gimping" iOS.