That’s not true. A Rino as an incumbent locks the seat up for many years — particularly Senators. They also (due to the nature of incumbancy) dissuade another Republican from running against them.
Look at Arlen Spectre’s career as an example.
“Arlen Specter (February 12, 1930 – October 14, 2012) was a United States Senator from Pennsylvania. Specter was a Democrat from 1951 to 1965, then a Republican from 1965 until 2009, when he switched back to the Democratic Party. First elected in 1980, he represented his state for 30 years in the Senate. Specter was a moderate who usually stayed in the political center.”
You want more of those or you want to give an honest conservative a shot at the seat?
Always support the most rightward viable conservative in every race. That's the Buckley Rule. In the Bevin/McConnell primary, Bevin is the choice.
In the General Election, Bevin is the choice in a Bevin/Grimes matchup.
In the General Election, McConnell is the choice in a McConnell/Grimes matchup.
In each of those three scenarios, the most rightward viable conservative wins.
Never vote for the Democrat, and never stay home and pout on Election Day because you don't like the Republican.