First, the Stormfather is a big enough spren to bond multiple people.Second, three were a common number of Bondsmiths, there could be more or less, although they didn't want to greatly increase their number.
Third, the Stormfather only spoke during Highstorms before Dalinar's bonding of him. Now that he is bonded, his presence in the Physical Realm should be stronger. Plus, Lift didn't speak with the intent of forming a bond.
Fourth, he did forbid all (honor?)spren from bonding humans. That may indicate some autority beyond being the biggest, baddest spren out there.