I think you're both right.
Tier points linked to credit card spending is indeed a unique feature. Albeit, ultimately, not necessarily a good one.
So whilst they run the very real risk of someone earning elite status by flying Emirates and Indigo a lot, with elite status on Jet being of increasingly diminishing value, I don't know if it's going to do significant damage.
By the way, isn't the Amex supposed to be the most expensive, and, therefore the most "elite". If so, wouldn't it make more sense to link this feature with the Amex instead? Or maybe they're going for quantity over quality here too.