Yes, the lander was around 100 kg, whereas RTG would weight around 40 kg alone. And it would anyway be needed only in this case of unfortunate landing in the shadow.
Once we talk about details it's clear how a lot of the complaints are based purely on a huge ignorance. It's good to ask to learn. But when somebody starts from the position that people who managed 25-year mission missed something to him "simple and obvious"...
