For me, it's the last 2 points for laptops that make it so that I don't see an iPad ever fully replacing one for me. iPadOS is just too limited and sandboxed. If I want to do something as simple as attach a file to an email from my iPad, the file has to be on a cloud service or in an app that my preferred email app recognizes and works with. Sometimes I even have to do it the opposite way and open the file in its app and "export" it to my mail app. On a laptop, I can simply attach any file from anywhere on my computer. Bottom line is that as much as I love my iPad for numerous tasks, there are some things that are very straightforward on a laptop that require convoluted workarounds on an iPad.
I find that more often than not, an email app should support the files app, which would allow you to access the file you wish to attach. Worst-case scenario is you have the files app open in splitscreen mode and drag and drop the file over.