“SPAs are far more complicated to write than traditional server-based applications, eating up more time and resources; the returns are highly questionable.”
My company has been selling Flash based SPAs for the better part of a decade. The returns are clear and proven.
“When your application grows to tens of thousands of lines of code, it becomes much more difficult to maintain, much more difficult to ensure a specific level of quality.”
Testability is also forefront in the minds of most of the people creating these new Node based frameworks. Our React code is imminently more testable than our Flash based code ever was.
“WebAssembly is coming, threatening to make JS irrelevant.”
Coming when? I have to build applications in the here and now — not the mythical time and place were 99% of my users have a web browser that supports WebAssembly. I mean seriously, that could take 5+ years. When it happens, there will be a new Babel plugin that will compile ES2020 down to WebAssembly. Done.