Why is Arceus banned in monotype?

Question

I made a steel type monotype team, and it said:

Your team was rejected for the following reasons:
•Arceus-Steel is banned.

Answer 1

Arceus is unlike other legendaries/Mythicals, in the fact that each of its base stats is 20 higher, equaling 720, 120 higher than (I.e.) Mew.

Comments

Thank u sir

Answer 2

III.) Broken - elements that are too good relative to the rest of the metagame such that "more skillful play" is almost always rendered irrelevant.
These aren't necessarily completely uncompetitive because they don't take the determining factor out of the player's hands; both can use these elements and both probably have a fair chance to win. They are broken because they almost dictate / require usage, and a standard team without one of them facing a standard team with one of them would be at a drastic disadvantage.
These also include elements whose only counters or checks are extraordinarily niche Pokemon that would put the team at a large disadvantage elsewhere.

source
Arceus fit that description pretty well, so it was banned.

Answer 3

Arceus is in the Uber tier, like many other legendaries. Pokemon in the Uber tier are banned from Monotype.

Comments

This is wrong. Galarian Darmanitan and single strike Urshifu are both in Ubers but are allowed in Monotype. Kartana is banned in Monotype but is in OU, not Ubers.