The Qur’an speaks of the importance of the Sunnah, for example:
(a) Allah says: “He who obeys the Messenger has indeed obeyed Allah…” (an-Nisa’: 80) Allah described obedience to the Prophet (peace and blessings be upon him) as being a part of obedience to Him. Then He made a connection between obedience to Him and obedience to the Prophet (peace and blessings be upon him): “O you who believe! Obey Allah and obey the Messenger…” (an-Nisa’: 59)
(b) Allah warns us not to go against the Prophet (peace and blessings be upon him), and states that whoever disobeys him will be doomed to eternal Hell. Allah says: “…And let those who oppose the Messenger’s commandment beware, lest some fitnah (trial, affliction, etc.) befall them or a painful torment be inflicted on them.” (an-Nur: 63)
(c) Allah has made obedience to His Prophet a religious duty; resisting or opposing it is a sign of hypocrisy: “But no, by your Lord, they can have no Faith, until they make you [Muhammad] judge in all disputes between them, and find in themselves no resistance against your decisions, and accept (them) with full submission.” (an-Nisa’: 65)
(d) Allah commands His servants to respond to Him and His Messenger: “O you who believe! Answer Allah (by obeying Him) and (His) Messenger when he calls you to that which will give you life…” (al-Anfal: 24)
(e) Allah also commands His servants to refer all disputes to him: “(And) if you differ in anything amongst yourselves, refer it to Allah and His Messenger…” (an-Nisa’: 59)
"And We have revealed to you the Book with the truth, verifying what is before it of the Book and a guardian over it, therefore judge between them by what Allah has revealed, and do not follow their low desires (to turn away) from the truth that has come to you;" (5:48)
Surely We have revealed the Book to you with the truth that you may judge between people by means of that which Allah has shown you; and be not an advocate on behalf of the treacherous." (4:105)
"And We have revealed the Book to you which has the clear explanation of everything and a guidance and mercy and good news for those who submit." (16:89)
"Allah is witness between you and me; and this Quran has been revealed to me that with it I may warn you and whomsoever it reaches." (6:19)
So the prophet settled matters and disputes based on the Quran. As far as everyday matters and specific matters then it was for those who were there with him just like those in charge of authority are for us now:
O ye who believe! Obey Allah, and obey the Messenger, and those charged with authority among you. If ye differ in anything among yourselves, refer it to Allah and His Messenger, if ye do believe in Allah and the Last Day: That is best, and most suitable for final determination.
So the questions like booty distribution of settling matters on the ground this was for the prophet and other people designated for that. But I am talking about now and not back then when the prophet was alive. All the prophets are to be obeyed:
Al-Shuara(the poets) Chapter
105 The people of Noah rejected the apostles.
106 Behold, their brother Noah said to them: "Will ye not fear (Allah)?
107 "I am to you an apostle worthy of all trust:
108 "So fear Allah, and obey me.
109 "No reward do I ask of you for it: my reward is only from the Lord of the Worlds:
110 "So fear Allah, and obey me."
123 The 'Ad (people) rejected the apostles.
124 Behold, their brother Hud said to them: "Will ye not fear (Allah)?
125 "I am to you an apostle worthy of all trust:
126 "So fear Allah and obey me.
127 "No reward do I ask of you for it: my reward is only from the Lord of the Worlds.
128 "Do ye build a landmark on every high place to amuse yourselves?
129 "And do ye get for yourselves fine buildings in the hope of living therein (for ever)?
130 "And when ye exert your strong hand, do ye do it like men of absolute power?
131 "Now fear Allah, and obey me.
141 The Thamud (people) rejected the apostles.
142 Behold, their brother Salih said to them: "Will you not fear (Allah)?
143 "I am to you an apostle worthy of all trust.
144 "So fear Allah, and obey me.
145 "No reward do I ask of you for it: my reward is only from the Lord of the Worlds.
146 "Will ye be left secure, in (the enjoyment of) all that ye have here?-
147 "Gardens and Springs,
148 "And corn-fields and date-palms with spathes near breaking (with the weight of fruit)?
149 "And ye carve houses out of (rocky) mountains with great skill.
150 "But fear Allah and obey me;
160 The people of Lut rejected the apostles.
161 Behold, their brother Lut said to them: "Will ye not fear (Allah)?
162 "I am to you an apostle worthy of all trust.
163 "So fear Allah and obey me.
176 The Companions of the Wood rejected the apostles.
177 Behold, Shu'aib said to them: "Will ye not fear (Allah)?
178 "I am to you an apostle worthy of all trust.
179 "So fear Allah and obey me.
All the prophets are to be obeyed and all are an inspiration and an example to us but they all are humans and they all follow God's revelation:
There is, in their stories, instruction for men endued with understanding. It is not a tale invented, but a confirmation of what went before it,- a detailed exposition of all things, and a guide and a mercy to any such as believe. 12.111
Here the Quran says about itself : "a detailed exposition of all things"
These verses you quoted do not validate taking anything that contradict the Quran or adds matters of deen the Quran never said. The hadith do contradict the Quran and do introduce religious laws not oitlined in the Quran. So what would be the purpose of the Quran then?
There is something I would like to add. When we say "Obey God and obey the messenger", this can only be done when God and His messenger are saying the same things. You can not obey the Quran and the sectarian Sunnah because they contradict one another. This is why Al Shafi believed the Sunnah abrogates the Quran but never vice versa. This means what they are really doing is just following THEIR Sunnah and not the Quran. You can't obey two sources that contradict one another.
Also not all Quranist are ideologues, many Quranist accept hadiths if it does not contradict the Quran. They just do not follow hadiths blindly. They compare them with the Quran. Many Quranist perform many of the rituals Sunnis perform, they just do not see it as the only way to worship God as the Quran recognized the Jewish community and the Christian community also. Rituals are a means to an end and not an end by itself:
It is not righteousness that ye turn your faces Towards east or West; but it is righteousness- to believe in Allah and the Last Day, and the Angels, and the Book, and the Messengers; to spend of your substance, out of love for Him, for your kin, for orphans, for the needy, for the wayfarer, for those who ask, and for the ransom of slaves; to be steadfast in prayer, and practice regular charity; to fulfil the contracts which ye have made; and to be firm and patient, in pain (or suffering) and adversity, and throughout all periods of panic. Such are the people of truth, the Allah-fearing. 2.177
Those who believe and those who follow the Jewish (scriptures), and the Christians and the Sabians,- any who believe in Allah and the Last Day, and work righteousness, shall have their reward with their Lord; on them shall be no fear, nor shall they grieve. 2.62
So it is not that all Quranist believe in one thing. Many Quranist accept hadiths, they just don't follow them like the sects do. Many Quranist pray 5 times a day, others pray 3 and others 2. It depends on how they interpret the Quran. But they all agree not to make something binding that the Quran did not spell out explicitly. Thats why Quranist tolerate each other much more than the sects do. Its not how your perform a ritual thats important but why and to whom. The pagans also prayed and offered sacrifices and performed pilgrimages, but they did it for other gods and not for God only.