Has anyone actually really noticed the performance of Stack Overflow? It feels like your average website before the JS bloat took over most “forum” style sites.
I wonder if they’ve traded off performance (and by the sounds of it, maintainability) with cost by squeezing all they can out of a minimal amount of hardware.
That's the difference between web development, "web2.0-style", and engineering. A web developer, when experiencing lag, will just add another AWS instance. An engineer will figure out where things are inefficient, and work against that inefficiency. You would be surprised how much of a performance boost you can get just by having good server-side pre-caching.
Also, consider that a lot of the lag you experience in the web today is actually caused client-side by excessive use of JS.
Engineering is a pretty slow-and-steady profession. Best practices, tests, and robustness are part of the point. There's an argument that a good engineer would know when those criteria are satisfied and so be more able to run up to the cusp, but I don't think it is fair to say engineers necessarily (or typically) work against inefficiency. Adding more AWS nodes might be the boring, prudent choice.
Redundancy is a form of inefficiency. Failure paths often introduce inefficiency. Well defined tolerances introduce inefficiency... even though you know those motors could handle a couple extra volts...
