No, the modern computers aren't that fast. Try running a BFS over a large matrix in python and then in cpp. You'll understand why perf matters. I realised this during one of my college assignments.
Your last paragraph is so true. I feel that's an issue we are facing a lot in every domain. I see people writing highly inefficient back-ends Because they believe anyways we are going to scale it horizontally, so it doesn't matter. The similar applies to frontends too I guess, people don't care to optimize apps either. They're like anyways the minimum configuration on which our apps run are getting better day by day, so why not build a resource hogger!
I personally believe we should start having "bootcamps" which talk about optimizations, and the cost of stupid designs. I'm also looking forward to compile time and run-time optimizations so that we don't even have to rely on the developers for it.