The thing to take into context is what the term Tohunga means to the Maori. To quote Wikipedia:
In the culture of the Māori of New Zealand, a tohunga ( tōhuka in Southern Māori dialect) is an expert practitioner of any skill or art, either religious or otherwise. Tohunga include expert priests, healers, navigators, carvers, builders, teachers and advisors. Blockquote
So in a weird sense the Matoran actually fit that very well, with the amount of expert builders and teachers we saw in G1’s society. However, the term Tohunga carries a sort of sacred weight to it, and that is where the cultural appropriation in Bionicle biffed it. From what I understand, the Maori still have people with the title of Tohunga in their society as a formal spiritual term as say Reverend, Priest, Bishop or even how secular terms like Doctor or Professor might be seen in western society. Yes, the Turaga maybe would have fit the norm of a real life Tohunga more; but it still messes with the issue that the title of Tohunga is revered and sacred to the Maori and there are still people working with the title to the present day, take for example Dr. Te Taka Keegan mentioned in this article who is considered a “modern day Tohunga” due to their knowledge in computer science and work in developing a Maori language keyboard with Microsoft. The Success of Te Taka Keegan – A Modern Day Tohunga | Scoop News
In short Tohunga is an honorific to be given to an esteemed community member in both secular and/or spiritual efforts, not one to be used for plastic Lego toys. Imagine if instead of Tohunga the natives of the island were called “Purple Hearts,” since that is a specific and honored honorific title in the US that we would consider to be “stolen valor” if anyone who didn’t earn it were to be using the term.
The Maori words that did remain prominent in Bionicle were much more appropriate to their real life terminology Toa being “fighter” or “champion,” Whenua “land”, Nui “great” etc. etc. My guess is that when Lego was faced with the lawsuit possibility that in their settlement that prevented the lawsuit they agreed to remove Tohunga to be able to preserve the other Maori words already in the Bionicle lexicon. Likewise, when Lego would borrow names from other languages in the future they did it from a mixed language source (like the MNOG II Matoran names) or from a very specifically dead language (Latin for the 2009 story) avoiding the issue of poaching so blatantly from one language and its regional neighbors.