You'll only need the expertise to perform in-depth optimization if you're scaling to the level of Stack Overflow though. For the vast majority of sites it won't be a concern. The simpler architecture should be the default because local method calls are easily 2 orders of magnitude faster than a network roundtrip (yes I know that's not the whole story). I'm not sure how or why creating clear boundaries without the RPC crutch suddenly became insurmountable.