As someone who does this sort of thing often, I would remark that the lines to buy tickets at the TGV station at CDG are often quite long, especially on Sunday. Especially if it is around a French holiday time. Sometimes the lines are long even if you use the automated ticket machine. And sometimes the trains can be sold out on Sundays.

The drawback to flying is that it is a very expensive taxi back to Lyon. And if you are going to the Hilton, there is no direct bus.

I usually take the relaxed route. I take the AF bus to Gare de Lyon (or the metro if traffic is bad). I have a very nice lunch at le Train Bleu, then I take the TGV to Lyon or Dijon or wherever I need to go. In fact I did this just yesterday and thanks to the lunch, I slept very well on the train.