(a) doesn’t bother me much, a quick drag of the divider can fix this
(b) however is a a pain, it’s at least a three-step process: 1) move one window somewhere such that it becomes an overlapping window, 2) flick the other window to the other side such that it resizes to become one half of Split View, 3) do the same with the other window
iPadOS should behave foremost as a system where windows/apps fill the screen automatically in some form (single app, tiled) with SlideOver or picture-in-picture as enhancements. There is nothing relevant on the “Desktop” that needs displaying. They could have made SlideOver more universal by having multiple SlideOver windows that are resizeable and can be placed in different locations.
One might say that resizeable and overlapping windows achieve the latter. But I think there needs to be a clear distinction between a base layer of apps that alone or together snap to fill the screen and windows that float above this.
Sure, if you use your iPad with a keyboard, pointing device and larger external screen, then a behaviour like standard desktop operating systems make sense BECAUSE you are using it as a desktop system and not as a touchscreen device anymore.
This logic also applies to the menu bar, it makes sense with pointing devices (the old target area with infinite height). When using a touchscreen, a toolbar with larger icons (as it has existed until now) works better. Yes, things aren’t standardised as to the shape of the icons, their placement and what is accessed via them. But Apple could have developed a new touch-based standard instead of falling back to tired old categories with a tiny font (because on touchscreen devices you don’t have enough space to spell everything out).