Namboothiris are generally thought of as priest because their predominant profession is preisthood inspite of the small proprtion of mailies that belong to professions like adukkala, arangu and Kadavu that donot study vedam.So that is why predominant profession logic compels  nairs to be classified as a martial class and ezhavas as toddy tappers. I have given below the different categories that namboothriri families fall in to based on their profession for substantiating this:
1.Aadu -They are specialised in Yaagam
2. Edu - They have the right to acquire knowledge and teach Sanskrit, Vedam, Linguistics, Astronomy, Astrology, Architecture and so on. 
3. Bhiksha (alms, symbolising a saint or a samnyaasi): They have the right to become a saint (or samnyaasi). 
4. Picha (also means alms, in crude form): They are Othikkans, helping other Namboothiris to perform rituals. T
5. Othu (Spiritual hymns): This class of Namboothiris was basically teachers of Othu (Vedam). 
6. Saanthi (temple priesthood): These Namboothiris are priests in temples.
 7. Adukkala  These Namboothiri families were specialists in large-scale cooking and catering.
 8. Arangu (stage): This special group of Namboothiris, called Chaathira Namboothiris, was a military group. Their evening entertainment was Panemkali (Sanghakkali). 
9. Panthi (dining structure): Namboothiris like Graamani, Thangal, Vaal-Nambi and Ashtavaidyans (all Mooss families except Vaidhyamadham) belong to this category. 
10.Kadavu (bathing points in the pond): Elayathu and Adikal are Namboothiris belonging to this category. Elayathu helps members of other castes to perform their rituals, while Adikal uses meat and blood to perform temple rituals.