Rules on shuffling are in the comprehensive rules book
"At competitive and professional level rel, players are required to shuffle their opponents deck after their owners' have shuffled them."
While you may not be gaining an advantage, a common definition of cheating, you are not playing by the rules. Any judge that approved of this is technique is actually wrong.
Another definition of cheating is: not playing by the rules.
At a pro tour, you have to display three seperate, unique, shuffling techniques for both your deck and your opponents.
I'm well aware of the comprehensive rules. Here is the relevant text from the rules, because you are not remotely accurate in your portrayal:
*Randomization is defined as bringing the deck to a state where no player can have any information regarding the order or position of cards in any portion of the deck. Pile shuffling alone is not sufficiently random.
Once the deck is randomized, it must be presented to an opponent. By this action, players state that their decks are legal and randomized. The opponent may then shuffle it additionally. Cards and sleeves must not be in danger of being damaged during this process. If the opponent does not believe the player made a reasonable effort to randomize his or her deck, the opponent must notify a judge. Players may request to have a judge shuffle their cards rather than the opponent; this request will be honored only at a judge’s discretion.
If a player has had the opportunity to see any of the card faces of the deck being shuffled, the deck is no longer considered randomized and must be randomized again. At Competitive and Professional REL tournaments, players are required to shuffle their opponents’ decks after their owners have shuffled them.*
You'll notice that any explicit shuffling techniques or methods required are not part of the rules, nor will they be (other than the note that pile shuffling may not be used exclusively). There is also nothing in the IPG about it either for Competitive or Professional REL. If you wish to read more directly from the Judges site, you can do so here (and you probably should, because what you posted is entirely fabricated).
What I described is functionally the exact same as picking up the whole deck, side shuffling a few times and then cutting it in any place. If your opponent is not cheating or manipulating their deck before presenting it to you for cut/shuffle, there is literally zero problem if you are not manipulating their deck illegally. I await a reasonable argument otherwise supported by the rules (or even basic logic would do).