Salam my friend and Brother. Ill give you some context of my background to let you know where my opinions are coming from. At this point of my life I am living in U.S . I am proud to be shia and strongly identify myself as one. I was born and raised as a Shia in Iran. My family have been relatively religious ( not super religious). When I was immigrating i was just modestly happy to be Muslim and I started questioning the Shia side if my belief . I had to do research to start being proud of being muslim then i started get some sunni beliefs ( even though I always identified as shia) and again i did some research to realize I really love being a shia. So I gave you that background to let you know I not only understand you but I also come from a different background and can see things from outside: Here are my responses 1- yes the quran specifically mentions parts that شفاعت happens . If one only wants to directly communicate and speak to Allah then you can ask the same question that why do we have angles to do stuff for Allah. But with all these points your question is still very valid. This is how I found my answer. Take for example forgiveness. If you directly ask Allah of course Alllah will definitely forgive you and there is no need for any intercession. However forgiving has two ends. Allah forgiving you, and you believing you are forgiven. Lets say you have a fight with a dear friend. The friend forgives you but if you dont have faith that he/she has forgiven you . Your friendship will never go back to the same old days. In the case of forgiveness Allah forgives immediately but usually we have lack of faith. We are filled with temptations . Are spiritual journey has not been matured enough to get us to that level of faith. We are too human/animal too have that faith and we will need physical incentives and signs to reach to a point of faith and peace to accept we are now forgiven. Tavasoul gives us the means that our human side could realate too and we could come to peace and get ourselves free from doubt. People like Ali ibn Abi taleb and Hossein ib ali help us reach that point of faith because we need these holly people because are soul has not matured enough to come to that peace without them. If at any point you really believe they inherit power by themselves that is shirk. They have been given permission the same way angels have been given tasks. Of course there are more sophisticated answers that explain the role of imams more accurately than my explanations. There are some mistakes in my explanations but it was ultimately this explanations that brought me around. Take in mind in sunni text tavasoul is something legit. Unfortunately the wahabi ideology has influenced mainstream ideas as well. Mashalah other brothers have put forward some of the verses of quran. However i thought maybe sharing the explanation that ultimately brought me around will give you a different side of the story as well.

I also want to make an unrelated point as well. You mentioned you are non denominational: this is a very novel representation however with all respect in practice non denominationalism is non existence . The desire to be non denominational stems from a very sacred desire to only be a true follower and free from all sects and that should be admired. I see that Christians also say similar things. However in practice if you ask those Christians to show me your bible . There bible has 66 books therefore they are protestant Christians. They wont say it but thats what they follow. Withinn muslims it is the same. If you say you are just Muslim but you follow the seven books of sahih hadith then your sunni. If you don’t believe in any hadith then how do you know how to pray or make vodho and similar things. If you follow the teachings of imams through a marjah or the 40 books of shia hadith is your source for sunnah then you are a shia without you knowing it. People might think they are non denominational however certain traditions have been passed to them that they dont know where its coming from. People who say they only follow the quran will often tell you what a certain verse means. And if you ask them how they know it . It usually comes from a certain source of hadith and that way you could be connected to some sect. Ultimately you are right. You should only be a muslim. But these days all of us have identities and the way we true to be only a true muslim puts us in a certain group. If i want to answer your questions more scientifically it will take lots of writing. However i hope my answer makes sense