This "platforms" versus "destinations" thing is one of the key questions digital publishers are facing. Currently, I think that you can't make a wise decision based on pure strategy, but should act tactically based on numbers and data. Ideally, you don't only have your own data - you could be doings stuff wrong - but also compare to others' experiences (I wonder how long it will take until all these huge traditional publishers form a strong alliance where they really share numbers and strategies - it's a matter of survival over competition amongst themselves). The Guardian chose to pull out of two majr platforms, Facebook Instant Articles and Apple News, because the numbers don't really fit. Will be very interesting to see how this plays out.