Source: bhuvanesh
Non tamiL roots
The 4 ancient siddhantha mutts ranabhadra,pushpagiri,golaki and amardaka were actually in north and not in tamil land.
Kamalai NjanaPrakashar, the guru of gurujnanasambandhar (the sthapakacharya of dharumai aadhinam) undegone study on siddhantha in gauda desa.
Diversity loss
Even in shaiva siddhantha there are different schools of thought. Post meykandar,other inner sampradayas started to diminish. many mathas accepted meykandar theology and some tradition just stopped
The meykandar school of siddhantha shaivam is called so because it’s dominant in the the tamil land. There’s a saiva matha named vallalar aadhinam they follow aikyavaada saiva.
Suryanar koil aadhinam belongs to skandha parampara and they give more emphasize to sarvajnanottara agama. They didn’t follow meykandar.their philosophy is nimitto upadana karana vaadha. After suryanar koil aadhinam was taken over by thiruvaavaduthurai aadhinam, it became a meykandar tradition mutt. They don’t follow the scriptures of shivagrayogin (the founder of suryanar koil aadhinam) anymore.
veLLALa dominance
Vellalas are very good in administration as they are land lord community. As there’s no successor in some mathas it was taken over by vellala acharyas. Also there are independent saiva mathas headed by other communities as well.
shivAchArya diminishment
All shivacharyas who do parartha puja in temple can give diksa and preach agama jnana. But today they were just limited to priesthood. Even today they give diksa to their own family members and to saivas in locality.
Koonampatti aadhinam is headed by shivacharya acharya.