I never said it should be more complex. It, however, should be also structured somehow. There is a persistence layer, models, collections, services reasoning about them and pipelines aggregating and rendering things.

Well written JavaScript is reasonably fast and it now makes sense to optimize transported information size. Many calculations can be done front-end side then, which accidentally is also more cost-effective, since data center usage is paid, while user CPUs are more or less free (and not doing much while browsing anyway).