All true. I agree. The core conceit of the game is the DM presents a situation, the player expresses intent, the DM adjudicates the outcome, with or without the input of dice. Anything past that isn't about right or wrong, just preference.There is. It's at the beginning on page 6. The players have to describe what they want the PCs to do. Then the DM narrates the result.
Grackon wants to make an athletics check to jump farther is not a description of what the PC is doing to jump farther. There's nothing there other than a description of a normal jump. Now, letting you know that the Grackon is rolling a log to the edge of the chasm to provide a higher push off point for his jump IS a description of what the PC is doing to be able to jump farther than normal. The formal should result in the DM stating that Grackon automatically fails to jump farther, not having described anything that would allow him to be able to jump farther. The latter is such a description and would probably be entitled at least to a roll, if not an auto success.
I prefer to have fairly well defined benchmarks as a way to inform my adjudication, primarily because I want the players to be able to make informed decisions both at the moment and at removed but relevant decision points (such as when choosing skill proficiencies).
But I totally get that other people like to play differently. I just don't like it when people assert one-true-wayism when that is clearly not the intent of 5e.