That article actually predates AD&D, and was published in a 1977 Dragon (or rather, The Dragon) article. The thing is, it was essentially showing that many of the things that Gandalf, ostensibly the very paradigm of what a wizard was to D&D's audience circa the mid to late 70s, could do were covered by fairly low-level spells. The point being that if Gandalf was of such a low-level yet possessed great power, then PCs should take seriously the notion that great power is more a matter of creatively using what one has available, rather than having tons of raw power at one's disposal. In essence, it was a check against level inflation, or what has been called powergaming or munchkinism in years since, or Monty Haulism, in which the DM granted great wealth and power very quickly. Another point is that Krusk wouldn't be plowing through Sauron's army like a harvester through corn; he'd be adjusted for inflation and only be 2nd level, maybe, in a world where Gandalf was 5th level. Or Gandalf and the orcs would be adjusted up for inflation to appropriate, present-day D&D levels.