Southwest points are exactly the same as money (in that three's a pretty steady relationship between how many points is needed for a flight vs how many dollars are needed for the same flight).

So it's cheaper (or at most the same) to simply pay for the flight, instead of paying for the points and then using points.

Southwest is not like miles-based airlines, where there is no particular relationship between miles cost and money cost, and thus sometimes you can come out ahead if you buy miles and use them instead of just buying the ticket with money. (But that's mostly just for business class or first class flights, at those airlines where buying miles can cost less than the actual ticket.)

But because Southwest has a direct steady correlation between points cost and money for a flight, you can never get a better deal with points than with money. The only way you can get a better deal is by spending less to accrue points, but obviously when you buy points you're spending more.