No, it is not.
Once you are in office have a major advantage in name recognition and in funding.
This makes any effort to unseat you an uphill battle. The longer you are in the harder it gets.
As the scales of justice are always tilted in favor of the defendant because of the enormous power of the state so the scales should be tilted away from the incumbent.
Term limits is one way to do that.
Well, as our Founders designed it, the involvement of the people with their use of the ballot box was considered to best way to keep elected officials in line.