He has stuck to a small number of core beliefs throughout his career - correct. However, in terms of his and Labour's recent policy efforts it has been quite difficult to know where he and they actually stand - the EU, trident, policing and spending in particular - all issues where there has...
The only slight issue with your analogy is that Ranieri had previously been there and done it with other clubs - in other words, he'd already proved himself up to the task. The issue with JC is that there's been no real evidence to suggest that he'd be any good as PM.