Your interview process is not far from the ones I've been involved in and I think you make a number of compelling points. The onus remains on the hiring folks to actually put in the work required to follow a sane process. I don't understand why you're blaming these platforms for teams having bad interviewing practices.
There's nothing wrong with hackerrank-esque platforms themselves. They're actually pretty sweet if you want to work through a couple narrowly scoped problems and get instant feedback while picking up a new language. There are even some diamonds in the rough that are actually decent multi-stage problems you can work through with a candidate during an interview. They make data structures and general code literacy more accessible to aspiring programmers, which is not a Bad Thing.
If hiring teams are attempting (and failing miserably) to use these platforms as a shortcut, that's on them. Their system may be busted, but coding sandboxes aren't forcing teams to not put effort into their hiring processes; that's entirely up to the folks making decisions.