Several Dragon Pass cults routinely play around with sorcery – Lhankor Mhy in particular. But the Knowing Priests are largely self-taught amateurs when it comes to sorcery. Temples tend to know a limited subset of spells and that’s about it. Knowing Priests are of course welcome to learn more – but remember, Malkioni wizards aren’t just going to teach their secrets to some barbarian scribe!
For most Lhankor Mhy specialists, sorcery is more useful than spirit magic, but that’s really what it replaces. Rather than Detect (Substance) plenty of LM cultists prefer to learn something like Reveal Rune or Identify Otherworld Entity or Geomancy.
Moreoever, very few sages are specialists in sorcery! Most are specialists in Reading/Writing, Bureaucracy, Library Use, and other Lores. Most temples have a symbiotic relationship with the local ruling cult (Orlanth, Yelm) to serve as the scribes, bureaucrats, and administrators of the rulers. Sure you can study sorcery, but first you need to finish writing the minutes of the last council assembly or research that report on the trolls of the Guardian Hills the king of the Aranwyth commissioned, or whatever.
The Malkioni are different. Their sorcerers – the zzaburi or wizards – are expected to be sorcerers first and foremost. The local rulers make sure that the sorcerers have what they need to focus on studying and casting sorcery. Their libraries tend to be narrowly focused on books about or pertaining to sorcery. They might be nearly useless when it comes to detailed histories or careful lore, but if you need to find out more about the Combine Technique or really want to learn how the Tap Technique works (in the hypothetical abstract of course – one does not ruin that which one loves!), that’s where you should go!
And when we think about numbers, there are some 45,000 sorcerers in Seshnela – all specialists. In Fronela, we have 145,000 people with a smattering of sorcery, but only 5000 serious specialists (but they are seriously good at it).
There are about 45,000 Aeolians, and 20,000 Invisible God worshipers. Let’s say 5% are sorcery specialists (probably high), that gets us another 3000 or so sorcerers.
In comparison there are over 100k Orlanth initiates in Heortland/God Forgot. That’s not Orlanthi, that’s people initiated into the Orlanth cult.