Not disagreeing with you, infact I support what you said because this whole argument is yours but flipped.
Champions with more reliable forms of burst/heavy damage (See

Probably not the best examples)
And ones with less reliable but potentially stronger damage (see
ap
)
Probably really horrible examples given the range / utility difference along with ability to aoe the enemy team but please bare with me.
What would be the point in playing a less reliable champion (that has more damage) if you could already easily burst and kill the enemy with your damage as a champion who delivers that damage reliably. (
isnt allowed to be buffed / even exist in meta most of the time because of how her R interacts with this statement.)
Say damage was increased by 100% (Because damage is kind of okay right now, this is just an apocalyptic situation)
Reliability, mobility, and range would all be supreme, anyone who needs to exist for more than a few seconds and land their abilities while also being immobile would be immediately out of the picture.
But that doesn't make you wrong, it supports your statement but from the otherside of the coin, if damage was decreased then your statement would start taking effect and unreliable champions might start ruling the game since they will have several chances in order to land their burst.
My point is there is two sides to this balancing act and the tree can lean either way.