At the time of writing this question, the Turkish referendum for changing the Constitution has just finished with approval of these changes (about 51% for "Yes").
According to this source, Turkish government has operated tremendous changes after the failed military coup:
Here are some more startling numbers, according to the BBC: 6,000 military personnel arrested, including more than two dozen generals awaiting trial; 9,000 police officers fired; almost 3,000 judges suspended; and more than 250 members of Prime Minister Binali Yildirim's staff removed from their posts, as have 1,500 Finance Ministry employees.
So, from a layman's perspective Erdogan and his Government already have immense power, as they operated a lot of changes in key positions. So, even without a presidential system, Erdogan's will prevailed.
Question: what is the purpose of such a referendum, if the power was already concentrated in Erdogan's and his Government's hands (or at least it looks like this)?