One thing that is sometimes hard for people who are used to systems with a lot “game balance” is that not all Gloranthan cults are equal in terms of importance, access to magic, or utility. Let’s quickly compare the cults of Orlanth and Yinkin.
Orlanth is a first tier cosmological entity, one of the Great Gods of Glorantha. He is the main Air God, the Thunderer, god of adventurers, tribes, and kings, who led the Lightbringers on their quest to Hell, and who contests with Yelm over rulership of Glorantha. He has more than a score of special Rune spells, more than a dozen major associated cults, and four major subcults. If you want your character to explore Glorantha’s magic broadly and deeply, there are few cults better to do that with.
Yinkin is a third tier cosmological entity, a minor god. He’s the god of shadowcats, a feline native to Dragon Pass that are long associated with the Orlanthi people. He has four special Rune spells, is associated with two major cults, and has no significant subcults (his cult is too small). He’s the god of cats, and just doesn’t provide a lot more than that. Heck, the only reason he has much of a cult at all is that he is Orlanth’s half-brother and accompanied Orlanth on many adventures – most people worship him as an associate of Orlanth.
However, BOTH cults can be equal fun to roleplay. Yinkin’s magic is limited and his power small, but it is fun to play the worshiper of a capricious and mercurial cat. And although Identify Scent is not as combat useful as say Thunderbolt or Lightning, it does have its uses!
Not every cult is going to be equal or anywhere near equal. Deciding to join the cat god cult is a player decision, not a GM. But you do what you want to do.