Sure, you can be fastidious and say that there is a kink, however indiscernible, in the actions of McGrath and Holding, but it's nowhere near in the same stratosphere of Murali/Harbijhan. Put simply, that's why controversy has dogged the Murali/Harbijan over the years, and why McGrath and Holding have unblemished reputations.
No it's because the optical illusions inherent in things like this when one can't see how an arm is reacting to stresses placed on it tend to bias things somewhat.
C_C is right; the degree of flexion for bowlers who had supposedly flawless actions and those who 'appear' questionable is around the same. The perception that one throws more than the other is just that; perception. To argue that a bowler's action is able to be determined 'flawless' with the naked eye is to believe that someone's depth perception and ability to withstand parallax error is flawless too. That's just dumb.
Not everything is down to science mate, some thing can only be seen by trying them in real life.
Excuse me?? You're not seriously going to argue that an imperfect human eye is a better measuring tool than high shutter-speed, hi-resolution cameras from several angles with a butt-load of computer power to back them up, are you? I mean, geez come on.........
The off break is a correct action as your arm stays straight through
As has been conclusively proven by the aforementioned human movement members at UWA, this doesn't happen for any bowler. EVERY bowler has a natural degree of flexion in their action.
If a bowler cannot bowl with an action smooth enough to be accepted by the umpire, he cannot bowl.
What you really mean to say here is 'if a bowler can't bowl in such a way that his action appears smooth enough to convince an umpire, he cannot bowl'.
McGrath and Holding are not chuckers because no umpire with even a shred of remaining sanity would call them for having an illegal action, because their actions are classical and flawless, whether their elbow flexes 1 degree or 20 in a completely unintentional manner without being visible to the naked eye. If a bowler jogs in a chucks the ball with 1, 6, 14 or 40 degrees of flexion on purpose and the umpire spots and calls it, he is a chucker. If he bowls a legitimate delivery with incidental level of flexion, he is not.
Both Murali and Harbi bowl with an unintentional flexion in their actions too. So why label them as chuckers?
Why is whether a bowler deliberately flexes a determinant for whether they chuck anyway? It's certainly not that way in the laws (the laws don't speak to intention, only the end result).
And calling their actions flawless has been, again, proven to be erroneous. For you to convince anyone that any human's arms remain straight whilst under stress (such as in delivery of a cricket ball), you'd have to first convince them that those bowlers' arms aren't affected by Newton's 1st Law of Motion, which they are. Even if they were robots with re-inforced steel for arms, there would be a degree of bending and flexion. Just because you can't see it, doesn't mean it doesn't exist.