Is bringing packs that have a higher chance of a mythic rare to a draft cheating?
Yes, it would be cheating. Your tournament organizer must either provide the booster packs or randomly distribute them before the drafting phase. If that does not happen and you try to exploit that fact, you are cheating.
Since you are well aware that your packs would give you an unfair advantage, you would be cheating. Whether or not your tournament organizer made it easier for this situation to occur by not pooling the packs is irrelevant.
From the Tournament rules:

7.3 Card Use in Limited Tournaments
Cards must be received directly from tournament officials. This product must be new and previously unopened.
If the Tournament Organizer allows players to provide their own product, that product must be pooled with the rest of the product for the tournament and randomly distributed.

The rules (Judging at Regular REL, Infraction Procedure Guide) don't cover your exact situation, because if the tournament rules were followed, it should never occur.
However, cheating is not allowed at any REL and must be sanctioned with disqualification. Going by the definition in the IPG, cheating occurs when a player does something illegal, tries to gain an advantage, and is aware of the illegality.