That'd be my final solution, yes. But I've been able to do this many times in the past, so why not now, is the question.Why not just skip removing them and then not need to install any GApps of your own at all?
Doing this way, it'd be a clean setup as removing every stock google and using only pico GApps. And maybe, just maybe, pico is in someway lighter/better than stock GMS?
Remember, removing stock Play Store & Services doesn't cause any instability, so wondering what's wrong with GApps not being installed, despite a successful flash.