Why all these complications?

The aggregator isn’t necessary, it’s just a convenience. It’s perfectly OK to subscribe to individual sites and feeds and being your own aggregator for yourself.

Also, why copy posts to your own site? No, it wouldn’t be proper syndication because the original post won’t link to your “syndicated” copy. Also, not all websites allow you to simply go and copy their content, legally speaking. And you don’t need it anyway; what’s the point? So that you read it on your own site? RSS readers have been accomplishing a similar task for ages now, and there even is a technology to track the changes in the original post — no need to reinvent the wheel. Of course, the RSS way of doing things comes with some limitations, for example, you don’t always have full content, and you almost never have fancy things like JavaScript snippets or crazy CSS formatting, but you weren’t going to copy random JS code from other websites to your own one anyway, were you?

A reader (to read what other sites published) and a publishing solution (i.e. your own site) are two very different things. You can, of course, have your website do both, but you don’t have to. And you don’t need to bolt them together simply to be able to do “likes” and replies while you’re reading (although you can, of course): having them interoperate (via MicroPub or some kind of hooks) is also a viable option.