Reviewers love this phrase and use it enough that it has become fixed and thoughtless. Aside from that, which is bad enough, I'm interested in the value of casting as an object of thoughtful criticism. In a perfect world, a theoretical theater fantasia, such a comment would be a laughable impossibility. Not because there would always be a "perfect" actor for every role, but because we would understand that the actor's craft means that any actor can play any part. The ideal actor is as good a Falstaff as a Hamlet as an Othello etc. I guess we know we don't live in such a world and so casting exists and casting directors have a real job and an important one and there is, I guess such a thing as a person who is "bad at comedy" or "not a leading man" or something like that. The problem is, the criticism "woefully miscast" I think, diffuses criticism and turns an active accusation into a passive. What the reviewer must mean is that the actor gave a bad performance, but for some reason is uncomfortable making this claim. People involved in the production of plays understand a bad performance can be the result of a lot of things: bad directing, bad writing, bad acting, an uncomfortable sweater, a cold, a break-up, maybe bad casting. What I don't like about the de facto criticism of casting is that it insinuates the critic as an insider on the process, it highlights the artifice, and undermines the actor's art.
Imagine the insult. Not "Actor did a bad job as Iago", but "Actor--no matter what--could never possibly succeed at this role. Anyone who thinks so is wrong, and they all wasted their time." That is woeful, and I think it is a much more difficult problem to diagnose than a bad performance. And much more difficult than one would guess by the frequency of its assertion.