Actually based on its latin root of Alumina, Aluminum would be the most proper spelling. The original discoverer of aluminum in fact prefered this initially although later agreed to use the aluminium spelling to conform it with strontium, potassium, etc.
And while there are more "ium" than "um" elements, that does not mean the others are "inconsistencies" since many of them existed as named BEFORE other "ium" metals were named. If we go by "there are more of x than y" as determining correctness, I assume that means you are willing to concede that by such logic American spelling and pronunciation is now in fact correct as the population of the U.S. is three times that the COMBINED population of GB, Canada and Australia and I doubt the remaining countries which speak British English as their primary language can make up the difference. Of course really by that logic, whatever the Chinese call something must be the official name, more people speak Chinese than any other language as their native tongue...
However BOTH spellings are considered correct, different countries prefer one to the other, but IUPAC has in fact recognized BOTH as valid. And no, the REST of the world doesn't do it "right" with the extra i, different countries do one or the other.
As for