There are gambles, yes, but they are
microscopic compared to retraining from one kind of engineer to another.
If you have n years of AS3 experience (n=7? Or what happened between 2012 and now?) and find yourself unable to compete with people with the same n years of iOS experience, I humbly submit that something else is wrong. Never mind that AS3 is a dialect of ECMAScript, which I hear is still used in a few remote pockets of the web, that hard things about programming isn't about the language and the framework, it's managing complexity. I struggle to see how retraining to iOS is going to take more than a few weeks of systematic reading and practising (possibly taken on your own time), and little more than a few months on the job to be on par with people who have several years of experience.
But more important is all the stuff that isn't about programming at all: Being good at organising your work, communicating well, testing, making sure you understand the entirety requirements as they are intended and that your delivery fully satisfies the requirement etc etc. Someone with n years of programming experience should master those things, and these count very heavily when picking people for lead roles.
Anyway, bottom line: the difficulty of switching from AS3 to iOS doesn't map to the difficulty of switching from nuclear engineering to environmental engineering.