I can see how popular free software can be more reliable since you have a critical mass that uses it regularly as well as can fix bugs as they come up. However,

I can see how popular free software can be more reliable since you have a critical mass that uses it regularly as well as can fix bugs as they come up. However, there's a bit of survivorship bias here. Free software that is unreliable may never reach critical mass in terms of user base as well as open source developers, i.e. a sort of "Great Filter" applied to FOSS