It does not reduces maintenance.

It absolutely does, package maintainers just have to maintain ONE package for all distros.

And it costs hard drive, and with heavy use, probably ram too

This isn't performance really, it's storage, and I don't think it actually impacts ram.

Maintenance is only reduced on the surface level. The complexity you don’t see as a problem is the actual maintenance problem. It’s not a problem only if you’re not the one dealing with integration, maintenance or security.

This is a case you're going to have to try a lot harder to make, I don't see what you're saying at all.