I mean, if you go by DMG guidelines, you get to refresh your ki points after every 2-3 combats. And a Monk can very easily do this at 6th:
I move up to target A and swing at it. If I hit, I attempt to stun. If I stun, I move to target B. If target is not stunned, either because I missed or it made its save, I swing again at it.
After 2 swings, I spend a bonus action and ki point to flurry of blows. Repeat above. Except I deliberately move to an angle where when I hit targets, they will be auto-shoved 15 feet towards other stunned targets if stunned due to auto-failing Dex/Str saves. If not stunned, they can maybe fall prone so I get advantage on my next swing.
On the 1st round of combat, what can easily end up happening is an entire encounter is stunned and in burst formation. That combat very well might be over. Yes, it eats up 5 ki points if everything goes right with 4 opponents. But that's a renewable resource in ki points.
If you live in a world where DMs don't follow DMG guidelines or they make huge maps with lots of ranged attackers to deal with the annoyances of spellcasters with large bursts, yes, the Monk is going to have some problems. But no more really than what any mostly melee attacker will have to deal with anyway.