He is indeed Islamist. And not just that. He is a profound fanatic and bigot. Yet you cannot really say EU ever did anything about it. Neither did the USA. From the beginning on, the two powers have been daftly turning a blind eye to his extremism or to his transition from a secular democracy to gradual Islamism. The USA did it by keeping silent all along and EU did it by not applying any sanctions, such as direct threat of halting the EU negotiations altogether. If they had done it, it would have been quite a well-founded action.
Indeed the EU has been Erdogan's strongest weapon especially in his initial years of power. Among his herd of sheep, he has been the "world leader" who achieved to bring the EU down to its knees. What has the EU done against Erdogan's attempted and successful rapes on freedom of thought, separation of powers and independence of media? Nothing. Here and there they issued some meaningless reports about "how evil the Turkish government was becoming" and they have had no impact.
Any strong supporter of the USA and EU should admit it. These two have added their pinch of salt to the shit soup. They made Erdogan possible by ignoring it, because he was too much of an obedient little Middle East doggy to give up on.