You're writing on a computer magnitudes faster than the fastest computers of the 70s, with significant compiler improvement to boot.
Until about 10 years ago, hand crafted Assembler was still faster than C, and the speed improvements were actually needed.
This "let's write a text editor which is pretty much an advanced nano/pico in JS and have it take up 145MB" is only possible when everyone has a supercomputer in their hands anyways
It still is, especially when it comes to vectorization.
What?
Setting aside the fact that this can already be done in numerous different ways on many platforms, how is this a win?
It's hard enough for developers to write correct code, let alone maintaining the correctness of that code while loading and executing unknown code from other parties (see web browsers, and the last 20 years of security bugs related to plugins, extensions, addons, etc).
Long answer: If Unix and C hadn't won the fight in the 1980s like VHS did, we wouldn't deal with such low-level bugs. It took 30 years, but we're finally getting CPUs (like lowRISC) that were inspired by BS5000 or i960 and the languages to go with it are getting mainstream. To be fair, had we as an industry taken security more seriously decades ago, we would have written critical pieces of the stack in a high-assurance Ada profile, and put microkernel design capability kernels into production. We can extend 1960s kernel designs with all kinds of features, but without a coherent design it's impossible to provide the same assurance. This is why it's great that we have L4 descendants that incorporate a capability scheme and also support a multikernel scheme (ala Barrelfish) for making better use of a cluster of cpu cores.