Note: preemptively stating that all of this is opinion.
Both are easy. I think ascending is a little easier for most people.
I think overall this is true.
The discrepancy increases the less theoretical you are speaking and the more of the nuances of the AD&D game you add. If you pretty much had your to-hit table (or ThAC0) and the enemy had their AC, I think the two options would be neigh interchangeable. The instant the game had "plus" 1 - 5 be a benefit to both armor's armoring and weapons' to-hit, a system with a positive-is-better attack and armor system seems to become more beneficial. Once you add in all the different places* where situational bonuses and penalties start to appear and you have to figure out what the +1 or -4 is applied to the attack roll or to the defense (and if you actually applied a -1x to the number for armor, because it was a +2 bonus to AC, not adding 2 to your to AC), then it really starts to be lopsided towards positive on both sides.
*vision, elevation, facing, or heaven forfend the weapon vs armor table (where every time we had to mouth 'picks are great vs plate, scimitars against bare flesh' to remember if a + was good for the attacker or the defender).
That said (and to finally address your point), while I think the case for ascending is strong, the overall effect is not. We all made descending work, many of us when we were 8-, 10-, 12-years-old. It wasn't hard, but it was a persistent minor burden we all put up with because that's the system we had. If TSR had put out an alternate Ascending version of the game(s)* along with the alternate language versions, I would have snapped them up in a minute.
*AD&D, but also 2e and the basic/classic line.
Surprisingly, climb walls is one of the few things where thieves have reasonable chance of success.
The 1e thief has a lot of problems. {long list of legitimate issues with the Thief}
So at minimum to fix the thief:
{long list of suggested fixes}
And honestly, the class still wouldn't be that good but it would at least be playable.
Quote edited for brevity.
Personally, for a long time I've felt that the splitting out of the 'dungeon-crawling adventurer non-combat skills' into a separate class was the primordial mistake in all this. I wish that, instead of introducing the thief class in Supplement I, Gary had introduced 'the thief rules' -- something where either everyone, or just a Fighting Man* (and the different abilities could be split between those two categories) could do climbing and hiding and detecting traps. Some of them would require 'armor no heavier than _____' to succeed**. Barring that, the Thief class should have just been a variant of the Fighting Man/Fighter class, with access to less armor, but getting the thief ability package alongside fighter hp, saves, and combat options. That (fighter offense, but lessened armor) would make them an interesting complement to the cleric, who got fighter-like armor, but inferior weapons.
*possibly 'and any future class which does not derive a significant portion of its power from the casting of spells' with some kind of rules for what that meant.
**or take off gauntlets or helmet to do, giving more reason for the 'attacking un-helmeted characters' rules to exist.