Hey, you made it a giant. How easy do you think that would be? In this instance it's his action, it requires a lot more effort than pulling a lever and is more akin to grappling than an attack.
The problem is using your action to knock the giant over is almost never a worthwhile use of an action when the warrior could instead attack the giant. Also the player wanted to attack and knock the giant over at the same time.
In both cases your words not mine, and it's a lot more likely than RAW, where you can't do it at all.
you were the one who said you wouldn't allow it for the whirlwind or would require a special feat to do it. You are the one who said you would require a Strength contest as an action to knock the giant over. I'm merely pointing out what that means for the player.
It wouldn't be automatic, I'd want a to hit with improvised ranged weapon with really short range. long range over 1, max 2 sounds right.
and now you have a situation where the action is unease still hard to pull off and no longer worthwhile if you first need to hit with an improvised range attack, then the target gets to make a saving throw. If such an attack used your action, you would be better off merely attacking.
But contrarily how long would a ruleset that covered these eventualities be? I used to play and run Chivalry and Sorcery when it came out. Land of the Rising Sun streamlined it somewhat, but it is clunky because it is thorough. And it still didn't cover your Giant example because it also didn't allow called strikes, largely because it had a similar philosophy with regard to hit points, but did split HP and FP.
I'm not really sure you are comparing apples with apples though, a cold spell freezing water is a reach compared to knocking a giant down by hitting it's knee? Is this WWE all of a sudden? Isn't the point of the wizard his flexibility?
And as that is my table, why are you bothered?
A rule set can cover all this and be quite small though. The trick is not to cover every situation, but to give conditions that make improvising easy to rule for the DM.
For example, Savage Worlds can do all of this very easily and has about 25% of the rules of 5e. This is partly due to called shots, but mostly due to Acrobatic and Smarts tricks and the Shaken condition. The shaken condition is a wonderful catch all condition that can be used to show that an enemy has been hindered in some way as a result of a stunt.
Also, 4e has significantly fewer rules than 5e, but it is also much easier to improvise these actions in 4e (they are all examples from my 4e games). This is for a combination of reasons. First, in 4e, the baseline assumption is that you can do something interesting every round. Everyone knows at-will maneuvers that are better than basic attacks. This means when you improvise an action that is better than an at will attack, you don't need to be unnecessary penalized. Additionally, you have encounter and daily powers that can be used as a trade off for particularly powerful improvised actions.
For example, the attack at the knees can be a basic attack that if it hits, you initiate an Athletics contest to try and knock your target prone. The whirlwind can be a close burst 1 attack that requires you to give up your encounter power to perform. The creating a patch of frozen ground can merely create a zone where any creature that enters gets an OP attack that does no damage but knocks them prone. The drink in the eyes could use the Dazed condition, a powerful condition that is similar to Shaken in savage worlds because it is super versatile without being overpowered.
My point is not that you were doing things wrong. Whatever works fine in your games is great. But for players who have a solid grasp on the math and mechanics of the game, they often find improvisation to be lacking because of the exact traps you fell into. A game with more robust rules for stunts that are balanced in the system as a whole typically leads to more and better improvisation. I am merely pointing out that I find 5es lack of robust guidelines has lead to far less improvisation in boy games I have run and games I have played in.
