There are a lot of things that contribute to how fast an app opens or not. It isn't always just loading the file, there are often things that the OS does to check the app for instance.
I've mostly stopped worrying about how long it takes to load an app. Usually the time I'm working with the app is significantly longer so, once it is open, the time no longer matters. I'll typically keep an app like the office apps open for most of the day once I've got it open as I will probably need to use it multiple time across the day.
If you are on Apple Silicon then universal and native is the same thing. (If you’re on Intel, universal will run while ASi native will not)
I cannot speak to your personal MSOffice launch speeds. Word and Excel launch more or less instantly for me (M1Max). The first time it runs after a macOS update takes about 6 seconds. It seems to be performing some diagnostics before being ready to use.