14 FC games, not really 'a lot more'. One season's worth, give or take.Because he's played a lot more first class cricket. Seifert is five years younger and has a lot more going for him, number one being talent. He's right up there with Brendon McCullum afaic. This would've been the perfect game to give Seifert some exposure against a proper attack, although in saying that he has already scored a ton against Pakistan before....
Look, maybe Seifert is the future and Blundell's not. Maybe you'd pick for the future, not for next week (that's what they're doing - they're saying Blundell is more experienced and if Watling/Ronchi were out, he'd be in). But it's fairly easy to see the merit of picking Blundell given his record with the bat was better last year and as I said, his keeper is renowned to be better than Seifert's. It's a split decision on how mature they are today, their run-scoring output in the longer form, and I'd suggest strongly on glovework. Blundell was the choice. All in all it's a fair choice, a close choice but fair. Not outrageous, Wellington bias etc.
None of this should be used to suggest I don't rate Seifert. He's clearly a talented guy, probably a higher ceiling than Blundell. He's just raw which at 21 is understandable. As was Brendon, which is why he wasn't looked at for higher honours in Tests until 2 years after his ODI debut (when I think from memory Robbie Hart had the gloves)