I don't think you're picking up what I'm putting down. None of these options actually do as good for your monk as proning and bringing a flying creature within range. Sun Soul doesn't get Sunburst until level 11 and it's pretty bad per-ki cost. Kensei is just being a monk with good range, that's fine but it doesn't exactly counter my point.
Unless you're bringing a flying creature within range of more people than just yourself, doing so is an absolute waste of time and ki points; keeping at range and killing the flying creature at range is almost always a safer (if slower) strategy.
Basic Searing Sunburst is free.
Radiant Sun Bolts is just as good (ignoring Stunning Strike) as physically attacking (you get the same number of attacks as using your fists or a weapon, including a equivalent to Flurry of Blows at the same cost as Flurry of Blows) at the same range FoUA / WW operates at.
Being a monk that's better at range (and at real ranges) than a normal monk with no cost is what I'd call excelling against flying enemies, which would be a direct counter to the title of the thread.
Knocking a creature out that's using a spell is possible with a 4-Element monk. It's called Clench of the North Wind and it automatically breaks concentration at range.
Clench of the North Wind is humanoid only.
I'm curious, have you looked in the monster manual to check how many creatures fit that description? All dragons eventually get with 20ft of a character. A wyvern gets within 5 ft. Pegasus and Perytons as well. All flying beasts. Animated weapons. Etc. Check them out. Even if they have flyby, the monk can ready an action for when they get close.
No dragon worth mentioning ever
needs to get any closer to a character / group of characters than their breath weapon's range + half their movement speed. Pride or other circumstances may
want them to do otherwise, however.
Wyverns are arguably not worth expending ki points over (just shoot them to death with a ranged weapon or- if you must- ready stunning fist for when it gets close). Pegasi, Perytons, and most other flying beasts are absolutely not worth spending ki points on, though admittedly something like a roc would be worth trying to prone.
Flying swords and animated objects either hover or can't fly, so trying to prone them is pointless.
Like, I'm not so worried about the damage at range, as much as I am about the fact that your ranged capabilities will always be worse than your melee capabilities as a monk by design. You don't want to just reach your enemy, you want to bring them down.
The lack of the amazing Stunning Fist is a big drawback to going ranged as a monk, yes, but otherwise it's almost trivially easy to make a monk as good (or better) at range as they are at melee.