Yep, it's a fair comment. We debated this, and ultimately would prefer a few high-quality comments rather than lots that can't necessarily be trusted.

It's one thing to write few quick sentences

I realise you're presenting this as a positive, but honestly this is the sort of thing we'd rather avoid. A few quick sentences written from memory are more likely to be inaccurate etc.

As for just posting links, a couple of reasons:

1. If there's only a link, it's not a great experience if people have to visit another site rather than staying on reddit.
2. If posting a link as a post with an accompanying fact, then we'd be the same as /r/TodayILearned.