It's a reasonable point imo - the pressure from within. I've already touched upon the old generation of Russians who won't readily forget the austerity, but what of the younger Russians.
It's true in the past that Russia has gone through several chapters of regime change, but it was always one oppressor replaced by another; just different bs. It's only since the fall of the Soviet Union that the 'ordinary man' has experienced some of the trappings of Western culture and opportunity; which they have enjoyed for a while now. Will the youngsters really want to lose most of that and accept the alternative?
Throw in the wonders of modern technology which make it much easier for the citizens to find out what is happening beyond their borders, whilst simultaneously making it very hard for the ideologues to brain wash or control the narrative, and there is the potential for protest to snowball.
I still think this is the best chance in the medium term but it would certainly come at a brutal cost to Russian civilians before a tipping point could be achieved.
However, how ironic it would be if a taste of Western decadence did in fact prove to be the driver for the downfall of Putin.