Could you please bring the authentic hadith that says "hold to the Quran and Ahlul Bayt" so that we can see the grammar? In arabic please.
And yes, I agree with you that "it was not a grammar mistake" as we shall see.
I'm waiting...
Suppose the hadith is what Shiites say it means. What merit does Sunni Rijaal system have at that point? None.
So it doesn't matter, I'm not getting into verification by your conjecture system of rijaal.
That said, I saw a whole debate about this in this forum, and there was nothing wrong isnad wise but rather the criticism was two fold:
1. The version in Sahih Muslim is more authentic.
2. That the singular usage of what he was leaving us rendered it grammar wise wrong.
That said, even the version in Sahih Muslim, is to be properly be seen what he is leaving us with. He mentioned Quran there as a guidance right, so it's about guidance, then emphasizes on his Ahlulbayt and reminds with God about them 3 times.
To mention Ahlulbayt a long side with Quran is not ambiguous, but give it more context, he reminds of his own Wilayah "Whoever I am their Mawla", which reminds in the way his leadership and authority complimented the Quran, and then says "Then Ali is his Mawla".
That is obviously linked to the issue of Ahlulbayt and their legacy, and then emphasize a particular instance of a member of Ahlulbayt.
We can by looking at all the versions conclude:
1. They wouldn't separate till day of judgment, when Quran ceases to have it's role as guidance anymore, the witnesses however are still used by God then and forever in heaven as leaders of people of paradise. This means there is a unity with Quran and Ahlulbayt, you can't approach one over the other, but rather they compliment each other in a way.
2. Because of that, the versions with "I leave that which if you hold on to, you will never go astray" - gain eloquence words wise, and compliment that they won't be separated.
3. The Wilayah of Ali flows with that, and to emphasize why Ahlulbayt is a unity, the Prophet reminds of his own role as authority and guidance with respect to Quran, "whoever I am the Mawla of".
4. Wilayah is contextual, the emphasis on Mohammad's own Wilayah and what he is leaving us as Quran and his family, it's clear.
5. I'm leaving you with.... is in terms of legacy of guidance. The context is guidance, because he mentioned Quran. The pairing and mentioning with Quran gives context and leaves question, what role then does his Ahlulbayt have with it. And Prophet to emphasize on that talks about his own Wilayah.
6. In many versions it is mentioned that he also asked the people "Am I not awla to believers then themselves?", and so this gives clear context to what he means by Mawla, and exact example of part of the relationship he has over believers, and so the Wilayah again is clearly not about friendship.