a billions dollars on simple solar panels.
I think it was entirely appropriate to work out how much power they needed, then provide a power supply capable of achieving that, using materials that were acceptable to the people paying the bills (NB : not America, in the largest part). And they did it using some of the most sophisticated solar panels to go into space.
If they had used a Pu-238 RTG (which for political reasons may have been sourced from our neighbours - the Russians), and some 60-90kilos of instrument weight had been rejected from the orbiter to allow for the increased mass of the lander+RTG, and the lander had then landed, bounced, landed upside down, and achieved only 10% of the science package, would you have like to defend the RTG decision to the court of public opinion?
Ah, hindsight - the only 100% perfect telescope!