Shaman are often depicted using only simple weapons. Ceremonial Daggers, Spears, Staves, but also the occasional hand-axe. So simple weapon proficiency makes good sense. Though maybe even make it a taboo for them to use more complex weapons. Not "Metal" like a Druid, but Martial. It's not that they -can't- gain proficiency, but maybe breaking taboos means you can't advance as a Shaman 'til you perform a cleansing ritual? Still "Level Up" your proficiency and HD but gain no class abilities.
Firstly I will say I do like your suggestions on how an Shaman/Animist/Spiritualist class could be developed and I've go no issue with use of the term generally (though as an Anthropologist my usual advice is to either be culturally specific or to use a broad english language term/phrase). However
1 In developing a fantasy version of Shaman one needs to be careful that they not fall into error of depicting the Shaman as a 'more primitive' approach to religious practice, which is where much of the error and criticism of the use of the term lies both generally and within Anthropology scholarship. Limit shaman to simple weapons because thats how they are commonly depicted treads that soggy ground. When lists like Kracheks which include everything from Amazonian to Navajo, Mongolia to Africa to Australia to Norse, Sami to Malay they are coding for 'exotic primitive' and very, very rarely include things like Anglo-American Mediums conducting seances or the Italian Benandanti (17th century, whose spirits would leave their bodies at night in the form of snimals in order to battle witches)
For the core idea of real world Shaman? Sort of. Particularly in Tunguska and Mongolia. Less so in other cultures, where they may largely exist as religious political advisors, medicine providers, storytellers, or hermit-like oracular figures.
But Shaman in fantasy can cover everything from Totemic Barbarian type characters to Norse Völva to Orc Shamans or Pseudo-Aztec Warrior-Priests to Elementalists calling on nature spirits to fight their battles for them, directly.
Runecasting, Reading Bones, Haruspex, even just reading Omens in the world. Any could be something a Shaman does to predict the future.
2 I'd argue here that the purpose of class design in a RPG concept is to define a core idea and not to provide for the wider scope of things - sure a traditional Tunguska Shaman can be a religious political advisors, story teller and healer, but so can a Bard. The distinction with Shaman, whether Tungusic or more broadly is the Trance-state interaction with spirits. as its core hook around which players can then layer on their own 'heritage' ie Healing, Augury, Spirit walking. That said I do like the suggestion of taboos being built in to the class too - which suggest Druid style limits or Warlock patron taboos.
Also I think that by concentrating on the Communing with Spirits element generally (including Victorian seances) you remove the primitivist exoticism that can creep in.
I would like to note, however, this important aspect: While there are stories of Shaman being shapechangers throughout various cultures they are typically -antagonistic- in that aspect. Or, at least, untrustworthy. It's only really in the Malay and Polynesian traditions that transforming into a full-on animal is considered an outright positive. Many other cultures use shapeshifting shaman as a cautionary tale.
I'm not sure shapechanging is considered entirely 'positive' in Malay/Polynesian beliefs either. I do have ancestors who transformed into fish and he act as guardians, but there was still a level of fearful veneration (they are still dangerous). And generally people who became Sharks or Eels or Pigs were dangerous and not openly welcomed into your home.
(It also amuses me still that amongst my grandmothers people we were told not to kill blowflies because they might have been sent by your dead ancestors to check up on you)
