> use the probationary period for what it's designed
This is probably fine in an environment where the candidate has lots of other options, but think about this scenario: a person applying to multiple companies, possibly rejecting some offers, possibly relocating or otherwise changing their life, accept that one offer, and then be let go in their first weeks. Changing jobs can be emotionally difficult and being let go even more. If you have to restart your job search, because you were let go during the probation period, all the other roles you have applied to might have been filled. On top of this, contrary to when you were looking for a job last time, now you're actually unemployed and potentially under pressure to find something new.
So, in essence I don't think this is good for candidates.
You obviously can't take the above in a vacuum and think it's fine. You could say the same for the advice of "give people work which resembles what the company does" leading to a situation akin to having interns doing minimum wage work for free, putting pressure on others as a result.
But as things stand, nothing is preventing companies from doing the above anyway. If they think you're a bad fit, they will use the probationary period to cut ties with you. This is perfectly viable today. Your example assumes current filtering methods do in fact increase the ratio of true : false positives, and taking some of them out would decrease that ratio. This is not something that has been proven, and I'd even argue it's something that can't be reasonably proven within the next few years. This is even worse when considering a few interview rounds can only filter for the most obvious dummies, but can't decisively tell you the performance of that individual a few weeks down the line.
What your example does show is how much power employers have over employees. It just isn't healthy for individuals to have to carry this amount of risk while corporates continue to reap the benefits.
This is probably fine in an environment where the candidate has lots of other options, but think about this scenario: a person applying to multiple companies, possibly rejecting some offers, possibly relocating or otherwise changing their life, accept that one offer, and then be let go in their first weeks. Changing jobs can be emotionally difficult and being let go even more. If you have to restart your job search, because you were let go during the probation period, all the other roles you have applied to might have been filled. On top of this, contrary to when you were looking for a job last time, now you're actually unemployed and potentially under pressure to find something new.
So, in essence I don't think this is good for candidates.