I hope you would agree that Isnad makes ahadith more reliable as there are many different people reporting the same event. In contrast, Quran contains the words of only Muhammad no matter where they come from originally. It seems more scientific to rely on Isnad than to rely on a single person's account.
Yes but the Qur’an does not say to trust Muhammad. It says to judge the Qur’an by the Qur’an (e.g. 4:82).
The “reliable” ahadith you refer to do not engender certainty, and thus again are disqualified by the Qur’an. One must accept the Qur’an before ahadith, and the Qur’an does not allow one to believe anything which contradicts, nor does it require any other source.
The so-called “mutawatir” ahadith (if you browse them) are actually mostly irrelevant to application of Islam. I have not found one necessary to believe in to run Islam.
Can someone bring me a mutawatir ahadith that is not supernatural, and is necessary to explain the Qur’an (without contradicting it)?
The other ahadith likewise have uncertainty, and rely on human opinion. Thus to accept them as law is to accept humans as God.
,Quran does ask to accept things based on someone's reputation - that of Allah who is most likely an imaginary character. Matching reports of real and living people should certainly be taken as more authentic compared to someone's edicts whose very existence is doubtful. Don't you think so?
Not in this case, because Allah’s reputation is the same as the Qur’an’s reputation. Again, Muhammad is not to be used to judge the Qur’an. These are entirely different concepts.