Part of the appeal for more sc justices/more house of rep members, etc is twofold:

1. It reduces an individual lawmaker's power and (in the house of rep's case) makes an individual rep much easier for the public to pressure as they will be beholden to fewer constituents per rep (less constituents, the less support you need in order to rally people to oust the incumbent).

2. It makes corrupting the government with money a little bit harder: more reps = more people you need to pay off, and it's not like every additional vote you need only costs $1 or smth, we're talking you need to get everyone enough money to keep them on board, which could be an extra couple million/billion than corrupting people now.

That being said: you're right, we need more than just that. We need avenues to hold votes of non-confidence (which will both allow us to get rid of bad/not helpful public servants, and also force politicians to stop straight-up lying on the stump). We need to institute public funding of elections to keep things both balanced and less-easily corrupted. We need to end gerrymandering. We need term limits.