Did emergence of the modern party system cause the decline in Presidential quality after Jackson?

[Aurelius]

As I've been on my biographical tear through the Presidents, I can't help but notice that the quality of the men who held that office took a sharp decline at the exact moment that Van Buren engineered the modern party system and then became the first product of that system to ascend to our highest office. I don't think it's a coincidence that all of our first seven presidents are consistently ranked in the top half, even those with major black marks on their record (Adams - Sedition Act, Jackson - Indian Removal). I've observed that those who came before the party system had a much more statesmanlike approach to the office, with much less resort to narrow sectional and ideological prejudices than those who came after them. I've been thinking about whether this is due to the emergence of the party system or some other factor, or a combination. Other factors: the first 7 presidents were of the revolutionary generation in some way, or presidents in the antebellum era were uniquely bad in some way due to some structural factor that disappeared after the civil war. Any thoughts?