I have no issues with the 5E monk. I agree it's a polarizing class in any edition but overall the 5E incarnation is pretty solid.
That said, I 100% agree that the monk needs a bit more ki at low levels and the Four Elements path is hot garbage.
I think the following points, which have all been stated before, have a fair amount of support:
A. The 5e Monk is a very good implementation for those who like the "D&D Monk." They did a good job. Not perfect- they didn't put it on steroids like some of the classes, but it is a great implementation of the D&D Monk Trope. It "plays right" if you like Monks.
B. Of the subclasses, the Four Elements is easily the weakest monk subclasses (and one of the weakest subclasses in all of 5e, IMO). The way that the 4E monk's "spellcasting" features (Disciple of the Elements) is powered off Ki, as are the melee elements ... doesn't work. At all.
C. The one recurrent problem for Monk it that the Monk and the Warlock are the two most short-rest dependent classes; I think a decent argument can be made that Monk is the most short-rest dependent. As such, if your DM is not comfortable with short rests, and you are not getting sufficient short rests, then the class is going to feel very underpowered. While JC has said there is no limit, the rule of thumb is that you should be getting two short rests per adventuring day. So, if you have a short rest problem, then simply multiply the Ki points by three (two short rests + long rest) and use them as a long rest resource. .....
If that is still insufficient, multiply by four as a long rest resource- and if that is insufficient, you have bigger issues playing that the amount of ki.
D. Finally, a big issue is that many people who play the Monk don't enjoy it because it doesn't play in the way they want. Which is fine! There are many classes that I do not play because they are unsuited for me. Beastmasters (pets suck). Druids (hippies stink of patchouli). Bards (should be killed and not heard). Not every class will appeal to everyone.
Monks are similar to a leatherman multi-tool. Sure, you probably want the specific tool for a job; but sometimes, you just want to carry a single tool that might not be the best at any thing, but can be pretty good at a bunch of things.
....and, to paraphrase the immortal Ricky Bobby, "Monks are all about speed. Hot, nasty, bad azz speed."