Worse Quality Teammates During Promos?

Pretty new to the game, so would like to know if this is my imagination or actually a thing. I feel like whenever I get to promotion matches, as well as the few matches afterwards, the quality of my teammates is significantly lower than when I am not in promos. Most recently, I found myself on a solid five game winstreak that boosted me straight to promos. As and Bs all around as adc, high kills, lower deaths, etc. +20-23 LP per game. As soon as I hit promos (for the 4th time I think to get to S4?), am granted my one free win. First game, I go 3/5/5, my vi jungle goes 1/8 in earlygame (ended 4/13), xerath mid wants to ff at 15 after he went 1/4 against a yasuo (ended 2/9). Second game, my jungler and midlaner get into an argument because the jungler was apparently autofilled, and the midlaner had taken ekko which is what the jungler wanted. Jungler picks shaco, earlygame goes great. Then midgame rolls around, midlane feeds a veigar two kills, jungle and support give the enemy jhin three kills, and we get rolled. I did badly at the end of that game as we were pushed into nexus, getting 3 deaths for no real reason or effect besides making my mmr worse, where I ended 4/9/8.

I know I am to blame at least partially, I know I could be doing better - but I definitely feel the quality of player I get on my team is far weaker during promos. Does anybody else notice this too?