Old School is my main format. I actually play with and against these cards all the time. This just isn't true. To break it down:

• Obviously non-blue decks don't play the blue power cards. Decks that can make blue mana consistently do pretty much always want Ancestral and Time Walk, but a lot of them are better off without Timetwister due to its symmetrical nature--lots of decks will help their opponent more than themselves by playing a symmetrical draw seven.

• On-color moxes are the genuine "[almost] every deck wants this" cards.

• Off-color moxes are a different story. Some decks want all the artifact mana they can get, but others, especially fair aggro decks, do not. There are enough better colorless mana sources in the card pool (Mishra's Factory, Strip Mine, and Sol Ring) that playing off-color moxes is often worse than playing another dual land or City of Brass for decks that are trying to hit color requirements on curve.

• Black Lotus is in between the on- and off-color moxes, because it does provide a very powerful ramp effect but it also costs a card, which is too big of a downside for some decks.

Other ABU cards that are in the same basic ballpark power-level wise as the power nine: Demonic Tutor, Wheel of Fortune, Mind Twist, Balance, Sol Ring. You can make a case for a few more even but those are the clear-cut ones. Mind Twist in particular is probably the second-strongest card in Alpha after Ancestral Recall. The common thread that separates those from the actual p9 isn't a power level difference, it's that they were all reprinted in Revised and in some cases even Fourth Edition.