You have not proven anything. Toomey was elected by a very slim margin and turnout in Philly was low. That’s not to say that PA is deep Blue state though. Liberal Lincoln Chafee is Gov. Elect of RI.
In 2006 the Dems ran candidates who sold themselves as more conservative in Red districts and won. If they ran as leftists then they likely don’t take those seats. If anything that shows that you have to tun candidates that reflect the composition of the voters that are likely to vote.
The composition of voters is not static but dependent on the candidate. Meg Whitman types cause volatility in that factor because having two liberals to choose from does not motivate conservatives to vote. When 40% of registered voters stay home, what does that tell you? Conservatives want someone to vote FOR.