AidenCanis
I say claim that the method to achieve a third maturity was created by Morgan Le Fay and that Merlin started a conflict with her to avoid the dark side having an advantage and because he disliked the idea of a younger more talented witch existing and showing him up as the start of the conflict. This would hurt Dumbledore's and Europe's reputation and give a bargaining chip that would allow Europe to start making Archmages again but, make an amended that everybody knows it so that the method doesn't die out a second time. Just forget to leave out the crystal stage.