One major difference between Charade and Hitchcock films

The Hepburn roll was written for a man but Grant felt it was ridiculous having a man his age pursuing Audrey. The script was rewritten and the rolls reversed.

Though a well-known Hitchcock trope, not all his thrillers feature an innocent man who gets into trouble and a mysterious blonde helper, do they?

Take “Frenzy” for example. The innocent hero Dick loses his estranged wife Brenda and his barmaid lover Babs, light-haired but neither blonde, while his blonde friend Hetty becomes an enemy. Or what about “Psycho”? The innocent hero Sam loses his blonde lover Marion and links up with her brunette sister Lila. Or again, “Dial M for Murder”? There the innocent hero Mark loses his blonde lover Margot for much of the film, his only helpers being the police.

Every Hitchcock film is rife with fetishes and obsessions (Women's hair, shoes, gloves, secrets told in bathrooms, dominating paintings of dead relatives, etc. etc. Also, a Hitchcock film usually has a strong psychological undercurrent. Charade is fantasy fluff of the highest order and a sheer delight and I suppose 'feels' somewhat like 'To Catch A Thief' but is not 'serious' enough to be 'Hitchcockian'.

"The Audrey Hepburn role, an innocent woman who finds herself in the middle of trouble, is always a male role in Hitchcock films"

In addition to the noted exceptions of Psycho and probably Frenzy, I would also argue the OP is wrong regarding most notably another Hitchcock film that Grant starred in, that being Suspicion. While some toying with the ending in that film made it somewhat less clear just how "guilty" the male lead was, clearly the female lead, Joan Fontaine, was very much the innocent woman in the middle of trouble (with Fontaine btw winning an Oscar for her portrayal, so it's hard to know why the OP missed that one).

I would also argue that Hitch's Shadow of a Doubt similarly shows the Teresa Wright character as the innocent albeit much younger woman as the one in the middle of trouble compared to Joseph Cotten's character in the male lead.

One might also argue that the female lead in Hitchcock's excellent Rebecca, again Joan Fontaine, was the one in the middle of trouble there, but so was the male lead, Larry Olivier, so that is a more ambiguous film. Still Fontaine's character is arguably the more significant in that film, so Rebecca certainly does not support the OP's point.

I would even argue Rear Window is a poor fit for the OP's argument, if only because it is rather ambiguous just how much Jimmy Stewart's character's voyuerism fits with being an innocent.

Finally I also think Marnie is a very poor fit for the OP's point. Sean Connery's character Mark has his innocent points, but he is clearly cast in the masterfully ambivalent role of if you will the helpful predatorm rather than an unambiguous innocent, while Tippi Hedren's title role, for all her criminal behavior, is really the innocent sufferer of past misdeeds.

In short there are many Hithcock films that do not fit the OP's argument.

The Lady Vanishes features an innocent woman who finds herself in the midst of trouble. And she's a brunette.

Actually one of Hitchcocks earliest films, "Murder", featured a woman who was being tried for a crime she did not commit.

For me personally, the major difference is that Charade is extremely witty and funny, while I've never found Hitchcock's movies particularly amusing at all.