> 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.