It's hard to gauge how much of his sales is because of good reception to his work. Speculators went nuts over Punchline and bought tons of copies assuming she was going to be this huge deal and the next Harley Quinn. Tynion's also introducing a lot of other new characters as well.
I'm not really a fan of the book at the moment, but I do hope the sales boost is in part at least due to people receiving it well and not just Punchline. From the few times I've met him Tynion seems like a genuinely nice person that has a passion for what he does, and we need more of that in the industry.