Those concerns are orthogonal to the type of mastery Rich is talking about. If neither of your developers has mastered software development, it doesn't matter

Those concerns are orthogonal to the type of mastery Rich is talking about. If neither of your developers has mastered software development, it doesn't matter which you pick - they're both going to need a lot of training and handholding. If they have both mastered software development, then you may as well pick the specialist if you have a specialised task, or the generalist if you have a general task. The point is that someone's ability to add business value (or practical value if you aren't in a buisiness, maybe artistic value in some settings) isn't a function of their programming languages and platform experience. Realistically, nobody has mastered programming because they 'know X platforms'. All that experience guarentees is that they can reach their skill cap really quickly in any setting. This means nothing. It might even be a negative value-add if their skill cap is low enough. More information is needed to say if they are good programmers.