Much of the security afforded by systems without too much market share is that they are not seen as a juicy enough target. But any juicy target in the hands of a regular user (not an enthusiast, not an expert sysadmin) will be exploited. The more flexibility the user has, the bigger the chances they will pick convenience over security making the system even easier to exploit.
There's no system that will make everyone happy so the interests of the many for security outweighed he interests of the few for tinkerability.
Maybe I'm an outlier in this, but I don't think Linux is for everybody, nor do I think it has any reason to try to be. Linux phones should be an option for enthusiasts and security researchers, IMO. At no point did I intend to imply that they were some sort of answer to the issue of security and privacy for the majority of people.
If anything I thought my comment implied the opposite, since the community is so heavily DIY that it's comparatively a Robinson Crusoe scenario.
There's no system that will make everyone happy so the interests of the many for security outweighed he interests of the few for tinkerability.