I think you are right. Only problem with Grubhub is, that they are just in the US. Now this may be a huge market, but it attracts loads of heavy-weight competition (such as Amazon, UBER, Google).
Other market players as JustEat and especially Delivery Hero are more spread over the world and therefore less at risk to be killed by one of the biggies.
Still believe that the marketplace model is undervalued. So: I bought GRUB at a larger scale a few days ago :)