The new windowing system is actually rather decent when used with a keyboard + all window tiling / maximising / app switching keyboard shortcuts memorised. Although the lack of Slide Over is still inexplicable and sucks.
The issue is that most people don't use iPads with keyboards. The windowing system in this case is then an absolute nightmare compared to what came before, as touch-based users were clearly a distant second thought when designing it.
For any HNers who don't have access to iPads running iPadOS 26 / 18, and aren't sure if this is just the "people on the internet hating new things" reflex (it really isn't), here's a side-by-side comparison that clearly illustrates andix's point[1]
[1] https://www.reddit.com/r/iPadOS/comments/1mq8sgd/old_split_v...