How did you come to this conclusion? Do you have a source?
Asking out of curiosity.
It depends what you value. 5e has always appeared to me to be an attempt to implement a 2e-like game with slightly more modern sensibilities on a near 4e engine and chassis (without the 4e DM tools). Which kinda makes it similar to 3.0's attempt to implement a 2e like game on a more modern chassis. (And, oddly enough, 5e casting bears more resemblance to 3.X psionics than it does to any other D&D magic system).
But then I maintain that 4e was a good implementation of at least one of the games 2e was reaching for - the larger than life action heroes with the grittiness 2e inherited from 1e dropped.
Look at the monk, what do you see
1) Enforced role, clear power source, AEDU structure, damage and AC expectations, planned flavor to crunch pipeline, clear narrative link to the world.
I don't know about you but
I see an enforced role including an extra damage mechanic even if they don't actually hold your hand and name the role, a short rest dependent class with several at will and long rest abilities (therefore an AEDU structure with some spackle over the top), use of bonus/minor/swift actions and disengages to allow for actual mobility and extra attacks, damage and AC expectations based on things like consistent extra attacks, damage dice going up and going up with some consistency and forced movement. It's a 4e class under the hood with decoration on top to make it look like a 1e class. And to be utterly explicit the monk's striker-style extra damage mechanic (the extra attack/flurry that starts right from low levels) is very much a 4e thing.
Of course they screwed up the damage expectations because whoever designed the 5e feats didn't quite grasp the concept of synergy (Great Weapon Master as a feat in isolation is pretty well balanced - the problem arises when you combine it with reckless attack or any other accuracy booster). And the monk gets shafted a second time over in D&Done because, being more MAD (Dex/Wis) the +2 ASI feat being a generally poorer option is a stealth relative nerf for monks. But not being done well doesn't mean they aren't there. Both early and late 4e had classes with significant math fails.
1) a smattering of class features unlinked to each other but linked to a single choice reference, many of them niche and applicable only to a certain style of play
... you have looked at 4e powers? Because
many of them, especially among utility powers, and especially for the monk get highly specific and situational.
and the remaining 2-3 features carrying the entire power budget that it makes the class hard to reflavor without houserules.
The 4e monk was psionic, and the way the PHB 3 was written spamming your most OP power based on points and short rest resources was how 4e psionic characters (other ironically than the monk) worked in practice. The only worthwhile class in the entire PHB3 was the monk.