iserith
Magic Wordsmith
Which I have - like everyone in the real world who ever jumped an unusually long distance, I do it by trying hard. (In the real world people have jumped unusually long distances without using pogo sticks, ramps, valuts, parkour or magical enhancements.)
Nonsense. A player who says "I jump" or "I jump as hard as I can" has described an approach to the goal of getting over the cavern, and has not said what skill s/he wants to use.
It then falls to the GM to adjudicate this.
Clearly jumping is an approach that can achieve the goal of getting across a chasm. The only issue between us is that you regard it as certain that, everything else being equal, trying to jump further than what the rules on p 64 permit will fail. Whereas I take the view that the presence of the rule on p 59 implies that unusually long jumps are possible but not certain, and hence provide occasions for the use of the ability check mechanic.
I've said several times now that jumping an unusually long distance is possible. But it requires an approach that the DM will accept. There can be no success or even uncertainty until that time. That is the way actions are adjudicated in D&D 5e. You may say that "I try harder" is sufficient. I do not judge that it is. Neither of us are wrong. What judgment a DM makes in this realm is unassailable preference.