Although I agree with the annoyance of accidentally opening something like Photoshop and having to wait to close it. But a good number of resources that is loading is third-party stuff that demands to be present immediately on startup as opposed to being loaded on demand. But whatever.
Paint has the same UI as what? I hope you're not comparing it to Photoshop or any other professional level software. I believe the modern version of Word is a good bit more than a glorified textbox.
But then you point out exactly why these programs load slowly in your last sentence. Maybe just start using less complex software?