In most of Glorantha, polytheism is the norm. Gods and spirits are acknowledged and worshiped at temples and shrines throughout the land. The same deity might be worshiped at different places, with different names (e.g., Orlanth, Ernalda, Yelm, Yelmalio, etc.), or the deity might be of purely local significance (e.g., Pavis, Zola Fel, Geo, etc.).
For most cults, there is no central religious authority to declare a local cult to be heterodox, let alone heresy. This is a hard thing for us moderns – who love to proclaim things as heresy – to get our heads around. Orlanth can be present at the Hill of Orlanth Victorious, and in Boldhome, and on Kero Fin simultaneously. He can be an agricultural weather god married to Ernalda AND a wandering warrior adventurer who romances goddesses and nymphs simultaneously. If you can wield Orlanth’s power, you have the proof that you are doing it right.
A few cultures have political institutions capable of declaring certain worship heterodox or even heretical. The Red Emperor does so with the Lunar cults – and several Lunar religious and philosophical movements have been declared heretical by the Red Emperor, most recently the White Moon movement. Previously, several schools of Illumination were declared heretical by the Red Emperor.
Same thing in Malkioni societies. Groups of talars and zzaburi regularly proclaim other groups to be heretical variants. The Rokari and New Hrestoli accuse each other of heresy, and both accuse the Safelstran city states of embracing all sorts of doctrinal wrongs.
But to most Gloranthans, this makes little sense. The proof of rightness is whether the god lends the worshiper his power. Beyond that it is merely a matter of local norms or the experiences of a hero who straddles the worlds of gods and men.
Is an initiate of Heler specifically an Orlanth worshipper who leans into Heler’s lore for aid and magic? (In other words much of their worship is expected to go to Orlanth as well as Heler.) Or is the initiate centering Heler at some cost to their worship of Orlanth? In Dragon Pass, Heler receives most of his worship as part of the Orlanth cult – probably 95% of all his worship is as an associate of Orlanth. But a very small number of people initiate directly to the Rain God. Heler gets maybe 5% of his worship from this. A Heler initiate is going to be subordinate to the Storm Voices and Wind Lords, and likely to the Orlanth initiates who are on their way to Rune Master. But as specialists in a minor deity they likely rank more highly than ordinary initiates, simply because they are more devoted to their god (and thus more magically useful).