This is exactly why ranked is so lopsided and weird and ultimately misleading.
Your mmr/elo does not reflect in your ranked standing.
its a facade and you cant see the actual elo, you just see the badge!
but what you do is, you scout the other team, find out tht there are to gold players on their team but only silvers on yours and you assume, even if it is just subconsciously, that the other team has an advantage when in fact they do not! but you get that into your head and therefore play worse and when you lose you blame it on the goldilocks when in fact it was actually you who lost because of a wrong assumption.
all that aside, when a silver one duos with a bronze 5 (has happened to me more than once) and you are up against a team with all silver 3's, even though the mmr average evens out, the bronze 5 more than likely is going to lose you the game.
I think Riot should forbid duoing across different tiers. my personal opinion though!