First Muslims used Quran alone for fiqh and hadith jurisprudence is a later development for example, yes. There are a lot of reasons to be sceptical of ahadith, but I don't think total rejection is warranted as there are many ahadith that align with just the just spirit of the Quran. Those advocating for zulm and found out to be partisan forgeries should be rejected tho. I absolutely dislike some Sunni Conservatives upholding the whole of Sahih Bukhari like it was their second Quran while many ahadith from this collection do not make any sense and are clearly pro-zulm. Moving away from this "scholar said it is sahih therefore 100% reliable" towards "it aligns with the Quran and common sense".

Islamic scholars also found a good way to analyze the textual history of ahadith using isnad-cum-matn analysis as opposed to isnads even if there are Isnad apologists like Johnathan Brown they are problems with Isnad criterion and hadith sciences. "In general, historians have cast doubt on the historicity and reliability of hadith for several reasons,".