@Mittineague interlining of pages is a very important metrics for SEO.
Discourse is weak in interlinking, please look at the below screenshot generated from moz, it is clearly saying Total Internal Links are only 6,287 which should have be quite higher as you mentioned it has 15,000+ url indexed in google.
I strongly recommend we should have some strong mechanism for better interlinking on topic pages like all the standard blogs has.