[JoshuaRLi]

Right, there's always going to be some additional cognitive overhead with every new tool you adopt. The question is how much you value its benefits for your use case, and is it worth those costs. If you're so used to find, and it works great for you, then keep using it! It's indeed more powerful and standard than fd, which I think is well-suited for vast majority of simple use cases (casual use).

However, here's my reasoning for the first of your questions, as a happy fd user who switched from GNU find. Maybe it can give you insight into why the UX is designed as it is.

The extension is distinguished from the filename because it's a common use case (-e jpg less keystrokes than -iname '*.jpg'), it's semantically separate from the filename (IMO) and therefore should not be treated as part of it. And unlike filenames, extensions most often do not need to be pattern matched. If you want to match multiple extensions, just repeat the -e flag e.g. -e jpg -e png.