I understand your point of view but you are too legalistic. Winning the general election means getting the upper hand in daily politics. It would be the beginning of a dynamic process which could lead to a change in the presidential office.
It is the opposite, tho. Again, you don't exactly know that is changed after the Referandum. You think like that;
"Oh, if they capture Parliament once, then it means people are supporting that ideology and will vote that ideology's representive guy in Presidency election"
First of all, people don't even know who are MP candidates in their own cities, for their own supported political party, yet alone each political parties. What does it mean? It means people vote for
LEADER of the political party. Not for MP candidates that they will learn their names when they get elected
Or not even after they elected. For example, i still do not know all names of MPs in parliament, from Istanbul's 3rd electional region, even though i live in here and i used my vote. Did you learn all the MP candidates' names and their life stories before going vote?
No.
That being said, only political party leader matters.
If one political party leader will also be a candidate for Presidential Elections => s/he won't be a MP, s/he won't be in Parliament.
If one political party leader won't be a candidate for Presidential Elections => then why would people support him/her?
It is a paradox. People are supposed to win Presidential Election first, to save his/her political life, or will be removed from political life.