I can easily recall discussions of how CR breaks down in 3e, where I was told that I didn't know what I was talking about, it was a great, robust, tool, etc. Now, the worm has turned.
3e CR is a good tool. It just has its limits; it's clunky, unwieldy, and the balance for many monsters sucks. On the other hand it's better than any tool that had previously existed in D&D that I know of.
4e, likewise. There are problems in 4e. You can't play a gritty or simulationist game with it. Some of it's silly. Some of it's unbalanced (*cough*Undead Encounters*cough*). Combat often takes too long and can bog down into a grind. On the other hand, the best way to bring the flaws of a system into sharp relief is to offer something
better. And to understand the flaws.
I suspect that when 5e is announced, we will be able to discuss the problems of 4e. In fact, I would suspect that some of the folks who stick with 4e will be surprised how some outspoken champions of 4e now are commenting on the obvious flaws then.
And I'll say for 3e it was a vast step up on AD&D. Few of the criticisms levelled by AD&D supporters hold water - and most of those that do are playstyle differences.
Something doesn't have to be old to be viewed through rose-coloured glasses. 4e has flaws, just as Pathfinder has flaws, just as 3e has flaws, just as 1e has flaws, just as all games have flaws. Talking about them openly can, in some cases, help the designers improve the model.
At other times, when based on false premises, it's just noise. For instance when you are applying the same assumptions to minons as to normal monsters. (I'm not saying minions don't have their problems - they are too easy to take out with AoEs by paragon, let alone epic for one - and can feel like a slog if you don't have blasts/bursts).
For example, I am told that the later monster books for 4e are much better than the initial MM......A direct result of noting the flaws of the earlier book?
Yes. Noting the flaws by means of playtesting and informed criticism. When I dismiss your criticisms, that doesn't mean I dismiss all criticisms. Just the ones that are from people who don't know the difference between a minion, a normal monster, a solo, and an elite.