Agreed, It’s the worst possible User Experience imaginable. But my 2 most recent mini-apps both have a 'processing' splash screen blocking the user partially for many seconds at a time, all the time. And although there are some good technical reasons to do this, it is mainly done by design.
Why? Well, it makes great leverage to push towards a paying account where the users pays to move processing away from his device towards the cloud or a server.
In an effort to make the wait less boring, I added some gifs, animations and tips to the screen. Similar to the indie hackers screen loader. But I wonder, could I get away with showing ads? Not old-school banners, but more modern and creative variation? A meme-like gif, a short, a quote, a video, … a few couple of seconds before the user is given the option to proceed, or the popup moves out of your way but still in sight? I know from data from my previous job that users accept this, but I’m hesitant to implement this.