As adult, would you rather spend the rest of your life working on English, or get it done in several years and move on to other things. That’s the cost-efficiency I’m looking for. Pronunciation is no cosmetic, just to wow others; it’s Science, the fundamental of a language. There’s no how perfect the walk is; it’s you either got it right or not. But of course there’s no conflict to pay attention to words and sentences at the same time. If you ask me whether it’s achievable or realistic, I’d say yes. If you ask whether it’s achievable or realistic to other folks, I cannot speak for them because it’s up to them to determine what they can or cannot achieve.