I sure do however because 3.x was the other way around from 5e & it put the burden of finding supporting rules on the player who tries to challenge the GM. You can see the first step in the direction of a trivial "I have a game to run, you can look for some supporting rules for your claim while I continue running the game. If you find any I'll look at it between sessions" statement from the GM.
It isn't a case of challenging the GM we are talking about here, but what the actual rules say. Sure the GM can set whatever DCs they like, they could make free climbing the North Face of the Eiger, DC 5 if they like but that isn't what the rulebook suggests.
You made clear that you don't have a firm grasp of the skill system you are trying to school people on when you didn't even recognize the dmg table section and claimed that it wasn't in "the rulebook".
That's because the vast majority of the 3.5 rules are in the PHB (which everyone has access to), with some additional rules in the MM, the DMG is mainly guidance, while it has useful information it is entirely possible to play without ever referring to the DMG.
Asking someone to find a 3.x rule supporting the GM's agency to do something like set DC and not expecting the rules to immediately shut down the charge only serves to underscore that.
Not saying anything about the GM's agency to set whatever DCs they like, I'm just asking for some evidence to your claim that PHB rules are just their for the players to have a spitball idea of the DC, and the the DC's were generally easy to make.
This is what it looks like when a system actually supports the gm's ability to make rulings based on the particulars of a scenario
- After turning to PHB page 61 ( chapter4:skills) to cut short this straw grasping & show just how far from a paddle you are in the creek of RAW you are it then took me less than a minute of skimming relevant headings to find that there is a "Difficulty Class" heading on pg 63 that contains the following sentence right near the section start "The DC is a number set by the DM (using the skill rules as a guideline) that you must score as a result on your skill check in order to succeed."
Right so the DC is set by the DM looking at the skill rules which are in the PHB.
- The rules being used for guidance are located in the DMG chapter 2:using the rules. Specifically the DC table on DMG 31, but also with heavy reliance on bonus types & DM's best friend. with occasional inclusion of degrees of success & degrees of failure (also dmg ch2 on pg33) Not the player's handbook .
So there is a bit conflict here between expectation, guidance and the rules. The rules for some particular skills could easily push the DCs into the 20 to 30+ range, while the guidance was generally avoid those levels of DCs.
They other problem is opposed skills, players generally only had a small handful of skill point to spend across an number of skills, but opposition NPCs in published scenarios often specialised their skills in the opposing skills like Sense Motive, Perception and the like. So if a player didn't focus they would fail in those skills at lot of the time (didn't help that NPCs were often higher level than the PCs in order to make them a challenge for a party of 4).
Certainly I recall published scenarios at the time where taking 10, would never succeed, and unless you had put all your skill points into a skill, and like had a positive attribute bonus take 20 would fail too. To be fair the game almost assumed taking 20 in a number of skills like opening locks.
My experience as a player and a GM (running published scenarios) at the time was unless you constantly upped your skills each level they quickly became irrelevant, and failure even with a character putting all their ranks in a skill, was common.