Keep in mind that when Allah said “whosoever rules by other than what Allah has revealed, they are Kafiroon…Dhalimoon…Fasiqoon”, He, Subhanahu wa Ta’ala, did not say “whosoever rules by other than what the scholars have deduced from what Allah has revealed…”
Even if you take the minority opinion that the kufr of ruing by other than what Allah has revealed is (unconditionally) major kufr that expels someone from the religion, you still have to realize that this can only relate to the explicit rulings in the Qur’an and Sunnah; the “nass” ayaat and hadiths about which there is no ambiguity whatsoever, and no room for differences of interpretation. We are talking about fiqh issues, we are not talking about formulations of ‘Aqeedah that were deduced and codified by scholars; we are talking about absolute rulings that are clear and obvious and not open to debate.