No more than any other western country usually being dominated more by one side than the other.
Germany has been run by a single party for the past 15 years.
Exactly. But it still isn't a single party country. A social democrat was chancellor for the 7 years preceeding that and Social Democrats have been part of the CDU led government.
Are you claiming that the SPD still wields any federal power?
I've moved out of Germany, but that is certainly not what I heard from locals.Given that they are part of a coalition government with CDU, I don't see how the answer can be anything other than YES.
The SPD hasn't truly garnered more votes than the CDU since 1998, and since 2013 they have been running 10 points behind them.
Doesn't matter in multiparty systems, really. In Denmark, the social democrats have been the biggest party since 1924, except for periods in the 00's and 10's. That doesn't mean that we haven't had many center-right governments.
If the GOP lost 3 presidential elections in a row at a 45-55 clip, would you be saying it's still a governing party?
Depends on how they do in the other branches of government and at the state level.