What are the benefits of pouring all of your Ki into Water Whip, as a Way of the Four Elements monk?

What benefit(s) does pouring all of your Ki points into Water Whip provide, as a Way of the Four Elements monk?

This question is a follow up to some efforts to improve the Way of the Four Elements monk choice as discussed here.

It gives you the best increase over your usual damage per Ki points spent

When you spend a resource, the question is never how much damage you make, but how much more damage you make than without this resource1.

As from level 5 you start with Water Whip from below your normal damage2, each ki point spent increases not only the absolute damage output, but also the rate at which your damage increases over your usual damage.

On 12th level

With your usual Martial Arts you do 28.5 damage (2*(1d8+5)+1d8+5). No KP spent (Base damage).
With Water Whip you do 16.5 damage (3d10) for 2 KP (WW damage).

So the increase is: $$\frac{WW - Base}{Base}/KP$$

For 2 Ki points you gain -21% damage over your usual damage output per ki point spent. (If you spend only 2 KP, you decrease your damage by 42%, -21% per KP)
For 12 Ki points, you gain 12.6% of damage over your usual damage output per ki point spent. (If you spend all your KP, you increase your damage by 150%, 12.6% per KP)

So the problem with Water Whip is that the more Ki points you spend on it, the better improvement each next Ki point brings. This favors spending all your Ki points at once.

1 this is why Divine Smite is great, and Mordenkainen's Sword is not
2 with Martial Arts, at 5th level it is 2*(1d8+4)+1d6+4 = 24.5 damage3, against 16.5 from Water Whip
3 You can and should use weapons to increase your damage output

• I believe many sources recommend it because it was a bonus action to use, before erratas changed it to an action. – Kuerten Aug 7 '19 at 18:19
• Flurry of blows is more damage per ki point. – Miniman Aug 7 '19 at 22:07
• The issue is that images are not very accessible. (Though I don't personally know how much more accessible MathJax is to screen readers and the like.) That said, it might be worth asking on Role-playing Games Meta if there is an easy way to automatically convert a table to MathJax. – V2Blast Aug 7 '19 at 22:10
• @Miniman not only is it more damage per ki point, it is on top of your usual damage, not instead of it – András Aug 8 '19 at 5:55
• So then why is water whip the best damage increase per ki point spent? – Miniman Aug 8 '19 at 6:31