If you win your promo game you will more than likely skip from Gold 4 to Gold 2 and then you will be around what your MMR is. Most of your games you get matched with Gold 2 - Gold 1 with the occasional low elo or duod low plat. The best thing you can do is stop looking at lolnexus or similar sites that tell you your team's ranks if it just tilts you. Outside of duos everyone in the game is going to be at around the same skill level on both teams so as long as you keep positively influencing the game you will win more than you lose. When your skill level is way above that of the rank you are playing against then what your team mates do means very little. Once you start to feel that you need your team mates to do 'something' to contribute to the win you will be pretty much within a few divisions of your true skill level / rank. Like lets say for instance your skill level is Plat 5, if you go vs Bronze and silver you can pretty much build and play like a troll and your team can feed but you will still carry because of the skill difference. Vs low gold it will still feel incredibly easy but you might have to play somewhat serious. By Gold 3 you will have to start building correctly and playing correctly but you will still win much more than lose, and then by Gold 2 / Gold 1 it will feel like you need to somewhat organize your team so that they can help with the victory.
If you are Diamond 5 then it is pretty much the same except you can troll build / troll play until Plat 3 and then by Plat 2 / Plat 1 you have to start trying and organizing your team. This is why when you see challengers do their smurf unranked to master climbs they are pretty much just messing around until about Diamond 3, they will pick unconventional things and play pretty trolly but until they get to D2 / D1 it will just feel like a stomp.