The Democrat/Republican party system is what gives incumbents such a lead over challengers. I don't think term limits are the fix, I think we need to change how campaigns are financed - because right now, the parties pick who gets money in downticket races, and incumbents have their own war chests. That leads to challengers being outspent.
I just keep thinking about how the national party rolled over for Dianne Feinstein in the 2018 senate election, even though she lost the support of the state party. No big democrats were willing to drop their support of her, and the national party wasn't going to spend money on a primary/general challenge to a seat that would stay blue.