I think that unfortunately for him, his support inside Russia was probably never high enough to seriously challenge the existing leadership.
Don't think noble causes. Think money, blackmail. When thinking of timing of his death think of what else was going on in the west at that time. Think Tucker/Putin interview.
Navalnyj had very low popularity at home. He was mostly a made up hero for the western audience.
Ordinary russians not only gave no-f-f about Navalnyj but considered him a traitor or a trojan horse.
If this quote is genuine, as opposed to wistful, it suggests Navalny's evaluation of Russia was that Putin couldn't, in fact, do whatever he wanted there. As best I can tell, such an evaluation would have been pretty damn close to completely inaccurate.
The choice to return to Russia as a catastrophically-failed gamble based on that premise is what makes the most sense to me.