I have never heard of Arda Güler before to be honest because i don't follow the turkish league but he seems to be a very talented and elegant player with a great technique. That being said I heavily doubt that he will get many opportunities to show his abilities at Real Madrid because he just has such good and experienced players in front of him. I can still understand though why he wanted to join Real. It is very likely that you get such a chance only once in your life so better try and fail than not to try at all.
You do not follow the Turkish League closely, but you have made a correct analysis. Arda Güler will enter into a very big competition in Real Madrid. Frankly, I am a Galatasaray fan, normally I have generally negative thoughts towards a Fenerbahce football player. But Arda Güler is a really talented football player. For example, if you look at the goal scored by Wales in his last national team match or if you look at the statistics that Enner Valencia achieved last season, you can form a better idea of Arda Güler's potential. If he manages to adapt physically to the Spanish League, he will be successful in Real Madrid. His mental abilities are very high.