"The fact that Samsung has little control over their own updates highlights a glaring weakness with Android - one never knows whether they will get the updates pushed by Samsung"
Except this isn't an android issue, same way it isn't a Swiftkey issue - it's a Samsung issue. Samsung made sloppy decisions when integrating third party software, Samsung are the ones who network and region lock device updates, and Samsung are the ones who decide to drop supporting year old phones.
Samsung have complete control over their updates... in reality they've spent a good amount of resources to add the capability to their update system to pick and choose which ones your phone will install - based on decisions like if it's signed by the operator that owns the phone, what region your phone is from, etc... rather than Samsung not having enough control, to get the utopia you're suggesting in android land we'd need less control - no 3rd party keyboards, updates to google keyboard pushed out by the only allowable app store on android (play store). Not just keyboard... we'd need it for everything - one unified platform that manufacturers are not allowed to skin / modify in any way other than that sanctioned by google. But then we have things like that, they're called iPhone, and to a lesser degree, WinPhones.