No. This is literally a documented thing. The CR system is mostly a suggestion and often barely more than an eyeballed approximation. It is bad and has been bad since 3e.
The CR system works quite well for me. I doubt that it's sheer luck, although I do have to adjust my xp budget based on the group. That's not a big surprise though, there are simply too many variables. But if I calculate a hard fight for the group? It's generally a hard fight.
That does not comport with how people have described it to me. I wouldn't know directly; my only experience is with the MM and everything from it has been incredibly boring to fight, whether because it is just a sack of HP or because it is stupidly, overwhelmingly OP and the only options are "die," "run away," or "run away but still die."
Some of the monsters are boring, sometimes DMs set up fights to be boring. I don't want every monster to have a hundred widgets and options.
Again, that has not been my experience, and the tools for developing new monsters yourself are even more disappointing (and usually just exacerbate the "CR is useless" problem).
Again, this is something that works well for me, although I have started using an alternate I found a while back on blog of holding. Your experience is far from universal. The DMG guidelines could be cleaned up, they aren't pointless.