To make an uninstall of course you need the msi db parts (but you wouldn’t need the entire binary content). To make a reinstall (aka repair) you DO need both the db and the content.

I haven’t heard msis being bloated. I assume they contain exactly what they need to contain (though unsure about compression methods).

In the past when storage was scarce it seems like a strange design but these days I can’t say it feels so wrong.