But are they really paying too much? I can't think of a lot of products out there, especially those that have a recurring subscription, that don't required some sort of database. So you need a server running a database anyway. It seems that the subscription logic would be a very negligible addition to the instance you have to be running anyway.

To me it seems like the only sweet spot for lambda on a large scale would be for those that have consistent usage of a small instance that have some extra functions that need to be highly scalable and are very inconsistent.