Ray,
The problem with rants is they can be incoherent, I initially thought you were talking about menus and commands, but now you seem to be just talking about the preferences setting process.
1. If it was a single preferences dialog with a list operating like the keybinding dialog then it would be far bigger than even your giant screen and need scrolling every time, on average half the list.
2. Leaving the scroll where you last left it is useful when you change the wrong thing and want to change it back, but otherwise its worse, you have to know/guess/randomly pick which way to scroll to find whatever else you want to change, up or down.
3. Scrolling with mice is (relatively) easy on desktops with large screens, but its a [expletive deleted] pain on laptops with touchpads, which also have smaller screens so need to scroll more, and a surprising number of people use those for development. Luckily Geany isn't likely to be used on tablets or phones where its all touch.
4. Other IDEs (Eclipse, vscode that I know of) do have a single dialog, but to avoid scrolling hell they are arranged like directory trees in file managers, the categories (and sub-categories where applicable) are rolled up and the user only has to unroll the category they need ... scroll to category, click expand, scroll through category, "damn wrong one", scroll back up, click unexpand, scroll categories, pick another and rinse and repeat. Its the worst of both worlds.
5. To be fair the Eclipse/vscode method is better when the expert user actually knows which category and sub category they want, but until then its a pain. But then that also applies to the tabbed dialog Geany uses, its easy to navigate when you know where you want to go.
6. As Mike pointed out, Geany is not _specifically_ targeted at novice users, expecting them to learn the UI layout over time is not unreasonable, and it is organised in a way that makes sense ... to the people who wrote it. And the people who contribute are the ones who choose the target users, and they have chosen themselves.
So essentially there is no good solution, everybody has one they prefer, but the only one that matters to Geany is the one somebody contributes to the project.
Cheers Grumpy olde guy Lex