Well i think Last Island is right here .. The problem is that Muslims now a days have very little if not proper knowledge of their Peers .. The different schools of thoughts are in no way to be criticized as they have their own background .. Sometime ago i also had the same question in mind and consulted a friend who had good knowledge about the issues .. He said that during the times of Prophet S.A.W many Sahaba were sent to different places for the purpose of preaching .. Some of them never returned to Arabia after that and were committed to their task whole heartedly for the rest of their lives .. So they were unaware of some minor changes in Islam.
The Prophet S.A.W for example had offered his prayers differently .. He performed Rafa Yadain sometimes and he did not do it later ..
And to answer the question, there is no set way of offering Namaz described in the Quran .. The source for us on this is the Sunnah of Prophet S.A.W and later the Imams who had spent all their lives in search of truth ..
If you follow one Imam, u can follow Islam properly .. Taking one from here and the other from there is bound to confuse the follower ..
The rest is that study your faith properly and u will get all the answers .. And pray for all of us that Allah guide us to Siratul Mustaqeem .. Aaameen

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You Have To Keep Breaking Your Heart Until It Opens .. !! Rumi ..