I think that's a fair comment. My counterargument would be that if the new way of building software proposed in the OP was actually a significant improvement,

I think that's a fair comment. My counterargument would be that if the new way of building software proposed in the OP was actually a significant improvement, someone would have built a new IDE with it, and eaten JetBrains' lunch. Instead, we got Atom; prioritizing pluggability/extensibility/hackability over footprint/latency. To be clear, I'm not arguing for a fatalistic position that "there's nothing we can do about it". We can, and do, optimize performance when required. I'm just arguing for a more nuanced appreciation of the cost/benefit calculation that's at play here. Either there's an explicit cost/benefit being done (e.g. a PM weighs the "go faster" story vs. the "add new widget" story) or an implicit one (app #1 prioritizes speed, app #2 prioritizes features, and customers vote with their dollars; market share reveals which is more valuable).