That basically begs the question of what I'm saying though; why should we expect that there is an "easy to teach" process that "works", for some useful definition of "works"?
Our desire for something to exist does not mean it does exist. I think a lot of the rhetoric around "fixing" interviews is making this fundamental mistake, where what is desirable is laid out, and then some process that will putatively lead to this is hypothesized, but there isn't a check done at this phase to be sure the desired characteristics can even exist.
It may be that evaluating human beings and whether they can fit into technical roles is just fundamentally hard. (I mean, when I put it that way, doesn't it sound almost impossible that it's untrue?) While acknowledging fundamental difficulty is not itself a solution, it does tend to lead one to different solutions than when the assumption is made that there must be some easy, repeatable solution.
I can sit here and wish there was some easy way to communicate how to be a full-stack engineer in 2019, but that doesn't mean that such a thing exists, and anyone trying to operate on the presumption there is is headed for the shoals at full speed. People who know such easy things don't exist may still wreck themselves but at least they aren't guaranteed headed towards the shoals.
(Or, to put in another really technical way, the machine-learning-type bias that somewhere in the representable set of interview processes there must in fact be a good solution is not necessarily true, and think there's good reason to believe it's false.)
So the only thing you really can do is ask objective questions or check technical skills. Thus the choice is not between hard skills or soft skills, but between hard skills and no skills because the soft part deteriorates extremely quickly and becomes essentially useless at scale.