I think it's neat that the affinity system can showcase some lore connections between horses.
At the same time it's infuriating that swimsuit maruzensky needs to have Seiun's ult, which means you're not ever going to get a double circle for her unless you own Seiun, Taiki, and Bourbon, and then do the entire lineage yourself grinding the shit out of G1s, and even then it might only barely get to double circle.