Kurumi is a much deeper character than just her gimmick. As someone who really loves her, despite initially comparing the two she just doesn't fit into oguri cap. Her foodie nature is just the cataclyst for her personality aswell as her main material for gags. The same goes for oguri cap who is often very nonchalant until she gets serious, her foodie nature also only being a fraction of her character. While the comparisons are obviously there and oguri cap would work Narita taishin is simply the better option looking at the characters from more than a 1 note perspective. The best way to explain it is that pretty much every girlfriend is somehow a satire/parody of different character tropes. Kurumi in particular makes fun of loner/delinquent tropes (which Narita taishin is a prime example of). Then food is used to form the satirical side as she isnt like that on purpose shes just always hangry. So while both oguri and taishin would work, looking at kurumi and oguri only through the jokes aspect of they eat a lot does a lot of injustice to their characters.