I am sorry to say that your understanding that Quran is difficult to understand is baseless based on this verse:
Allah has promised that Quran has been made easy to understand. The following verse is repeated 4 times in Surah Qamar (55:17, 55:22, 55:32, 55:40)
My dear friend if you cannot understand Quran then it does not mean nobody can. You will understand it if you pay more attention and use your own brain instead of just being
a lamb and follow blindly what has been fed to you for centuries . The truth and beauty of Quran has been hidden by mullah for centuries from masses saying the same thing you are saying that it is not easy to understand and it is a professional job to understand it.
The difference between you and me is that I try to understand using my own brain and with a critical eye on the older interpretation but you take all that as is what others have been saying for ages.
As for sahaba saying to prophet , Allah and his Rasool know better , as per my studies and research it was their style , they knew that if Rasool( SAW) is asking a question it is to teach them something , not to test their knowledge or memory. So for example if Rasool asked them which city it is , Rasool(saw) knew which city it was and so the will reply Allah and His Rasool know the best. Moulana Moudoodi has discussed this style at length in Tafheem ul Quran . I guess you did not read it , looks like your knowledge and understanding of Quran is limited to one book or some lectures.
Now I come to questioning ahadees contradiction and answers given to them previously by scholars not all contradictions have been answered because there were very few people who would object to what was in the book of ahadees , again they would blindly accept like you what mullah told them they will not critically evaluate what he said..
To understand ahadees you do not have to be go to a madarsa , you have to study , study and study, which I do and try to spread the truth. Also whatever answers have been given in the past for the contradiction of ahadees , they are not satisfactory for me and for others like me.
Now to the subject of only Allah’s Authority for declaring haram there are many many verses of Quran which categorically state that only Allah can declare haram , no human has the right to do so.
Consider the following verses:-
"And say not of what your own tongues pronounce, the lie: ‘This is haram, and this is haram’, inventing against Allah a lie; verily, those who invent against Allah a lie shall not prosper. " 16:116
“O ye who believe! Don’t make haram which Allah has made lawful for you, nor transgress (or commit excess); verily, Allah loves not the transgressors.” 5:87
““Say: Bring forward your witnesses to prove that Allah has made haram these!” But if they do bring such witnesses, bear thou not witness with them; nor follow the vain desires of those who say Our Signs (revelations) are lies, and those who believe not in the Hereafter, or those who for their Lord make equals.” 6:151
“Say: My Lord has only made haram abominable (shameful) deeds, the apparent and the concealed, and sin (errors), and greed for that which is not right (trespasses against truth and reason), and associating with Allah that for (or to) which He has given no authority (or power), and saying about Allah that of which ye have no knowledge.” 7:33
“He has only made haram for you carrion, and blood, and the flesh of swine, and that which is devoted to other than Allah; but he who is driven thereto (forced by necessity), neither craving nor transgressing due limits, then verily, Allah is Forgiving and Merciful.” 16:115
And last but not the least this verse is a proof that even the prophet cannot make anything
Haram for himself let alone for others:
يَاأَيُّهَاالنَّبِيُّلِمَتُحَرِّمُمَاأَحَلَّاللَّهُلَكَتَبْتَغِيمَرْضَاةَأَزْوَاجِكَوَاللَّهُغَفُورٌرَحِيمٌ
**“O Prophet! Why holdest thou to be forbidden that which Allah has made lawful to thee? Thou seekest to please thy consorts” **
(66.1 Surah Tahreem verse 1, Yusuf Ali’s translation).