"be hugely costly and still only result in a license that isn’t immediately transferable to other countries (eg you have to hold a license for x years before you can drive abroad and/or older than x years old)"
So I'm going to ask again, what kind of countries issue you with a licence that isn't immediately transferable to other countries? You can get an international driving permit literally the same day you pick up your regular licence, there is no time limitation on that - or if there is where you live, please educate me so I know better.