problem is, you can and often DO have moron's writing installers. so you install 12 at once? big deal? which one was the one that screwed up your windows os install? you can't tell. it's not a good idea, ever.
take it from me, I have about 2 decades of working knowledge regarding creating/debugging installers
guess what? if your stupid windows update is running, then you try running installs, get ready to wait for up to DAYS for it to complete. Still think it's a good idea? I see this crap every day in testing so don't tell me any different please.
7 zip is one of the most primitive installers I have ever seen and tested as well, your test is FLAWED. Install huge apps all at the same time and see what you get.