Important Disclaimer - 1st edition Advanced Dungeons & Dragons is a masterpiece. It is still one of my favorite RPGs and is one of the most important games ever published. Because of my love for the game, it would be too easy for me to come up with 101 things I like about it so I am challenging myself by trying to come up with that many complaints about it. This does not reflect any animosity toward the system or the artist, rather the opposite.
I'm a thief-acrobat! What makes this especially odd is that I don't steal, I'm in the 1e age category for middle age, and am not in particularly great shape. Yet according to Unearthed Arcana , I must be a thief-acrobat because I can easily make a standing broad jump of 6' and UA page 24 states that non-thief-acrobats can high jump 3', running broad jump 8', and standing broad jump 4'! Now to be fair, I wasn't wearing to much in the way of bulky armor or weapons at the time, but UA clearly states that "no extra weight or bulky armor may be worn when high jumping or broad jumping."
Unless you envision the average AD&D adventurer as resembling Chief Wiggum from The Simpsons, there is a huge problem with these numbers. I gave my standing broad number, not to brag (the three jumps I made are nothing to brag about) but to demonstrate that an out of shape, middle-aged, non-adventurer can easily match what are supposed to be extraordinary abilities. These abilities doomed the class, but gave a lot of laughter to gamers who were jr. high or better athletes. In order to accept the class, you were pretty much obligated to accept the humorously bad non-thief-acrobat abilities. Even if one were to try to rationalize these abilities by assuming all AD&D worlds were higher gravity than Earth, you'd end up with more problems with crossbow ranges.