It's both, isn't it? Those two positions aren't contradictory - it is possible for a new manager to have a positive impact and begin implementing his principles of play, but equally, his work cannot be properly judged until he has been in position for a longer period (and ideally had a chance to get a few of his own players in and taken the team through a pre-season).
You'd expect a really top manager to have some positive effects pretty quickly and it's fair to praise them for those changes, but you can't judge them too harshly for those problems that they have failed to immediately rectify (particularly if they are contending with a congested schedule resulting in limited time on the training ground).