You're also not taking into account all the players it helped. Before this exploit happened, Alexandrite supply was low and everyone that wanted to make a Mythic had to compete for what little supply was there. I have to imagine multiple players even bought from other servers because their server's supply didn't meet the demand. That shouldn't be happening.

But with this exploit happening, the supply rose and the idea of making a mythic became a reality for more people, especially with the prices (slowly) dropping. I can remember multiple instances where people were shouting to buy Alexandrite and competing with each other just so they would get to buy it instead of the other person. Once again, a supply problem that shouldn't be happening.
Whether you agree with the amount of supply or not, it's as it is by the design of the devs. The quality of the weapons are based on the difficulty to obtain, if the devs decide that too many people now have mythics it will mean that when they get updated again they will be be nerfed back based on too many being available.

Devs always base the power of an item on difficulty to obtain and number of the items in-game.

More mythics = less impressive updates when REM are updated next time. You can say no but why else would they be limiting supply of alex as much as they are?