These should be taken as the hypothesis statement at the start of an experiment, that will or won't be borne out by what actually happens. Show, don't tell. One reason: People can be wrong about themselves. Or they can, with varying degrees of either idealism or self-dishonesty, present a rosy view that amounts to little more than a sales pitch for themselves. If it's true, you'll find out soon enough. If it's not, y…
Too many teams I have worked in have way too little personal on-boarding in my opinion. At least with these presentations I know how the manager "wants" to present him/herself, if this turns out to be false, as you say, I'll know soon enough.
On the other hand there are managers that do not introduce themselves enough to new employees which forces you to effectively learn by trial and error how you should interact with them.
My point is I would appreciate an idealist sales pitch about a new manager more than just an unplanned, informal conversation.