But it doesn't make sense what so ever. Your example of "creates more strategy for 2v2" is also just wrong.
Every card has a skill floor and skill ceiling. Every card also has a certain strength. If you want a card to stop appearing so often, you either increase the skill floor, decrease the strength of the card, or do both. Your change already decreases the strength of the card. Making it have the limits of a mythic does nothing but hurt build variety and make the card less viable in certain decks for the reason of limitations instead of strength.
For example (this example may not be the best, but it gets the message across) let's say that Sicklebear, GLS, and Magis are all in a perfectly balanced state. Let's also say that all of these generals have good splash damage. In this example, I would choose the general that best fits the other cards in the deck, but I could choose any of them. Your nerf of making GLS a mythic should not happen, and rather they should just nerf GLS into a balanced state where you choose to not bring him because you want him for his role.
That example might not have been worded properly what so ever, but eh.
The 2v2 claim doesn't make sense either. If the GLS player wants to bring Glacial Fletching, let them bring Glacial Fletching. You can still have that extra planning with a teammate where they bring Glacial and you bring something else (another mythic, a spell, etc).