Russia just got a considerable motivation boost due to sanctions so the local order book for SSJ and MC families will be likely on the scale of hundreds of aircrafts. They are no longer a prestige project and Russia has the track record of building the necessary industrial capacity quickly (they ramped up military production to support war in Ukraine far beyond of what the West thought was possible in that time frame).
I wouldn’t really call it disruptive; they’re using Russian aircraft because they have to. Anyone who has a choice in the matter will still pick the duopoly because of better dispatch reliability and fuel efficiency.
C919 isn't China's first attempt. But they have a long term view of the industry and should be able to make progress even if they only satisfy some of their own domestic demand.