The problem is that idiomatic JS and blazing fast JS are diametrically opposed to each other, in practice the latter is more like a bad C dialect. You're not allowed to allocate GC objects in fast JS but the language doesn't have good non-allocating alternatives. Nobody is actually going to make a complex JS app where all memory allocations are pointers into a giant ArrayBuffer, it's easier to just switch to WebAssembly at that point.
If JS had typed structs (like they have type arrays) it would definitely be more convenient.
However, that's not where the problem starts. A lot of web sites are slow because they simply run too much code that doesn't need running in the first place and allocates objects that don't need to be allocated.
We don't need lower level constructs if we can simply start by removing cruft and be more wary of adding it. Go back to KISS/YAGNI.
