There is an Elo Hell. Its -200 Elo from where your really suppose to be. -200 from elo says, "your just not good enough to carry these downs kids so you lose" To gain elo you must, and i quote RIOT on this, "be head and shoulders better than your current elo"...which really defeats the purpose of elo anyways, cause your really suppose to be playing in a "bracket" or "elo" based on your current skill level, which isnt the case here.
Winning your lane is simply not enough. Cause while your 4-0 the other downs kids on your team are 0-8 and the bruiser in top lane is now gunning for you cause he knows its a race between you and He.
Again, There is an Elo Hell. Its the place where your just good enough to be but not good enough to pass because its a team sport, not and individual one.
As for going duo, i have played with really good ppl and i've seen no difference in win ratio between the two. Im sure duo is better cause you can coordinate better. but i just havnt seen it in the win ratio for myself.
there is also a big difference between the brackets. >1250 you have people who just are now starting. Some have never played before and have never experienced ranked. Alot of them dont know the current meta so they choose really aweful champs that do not mesh well with the team. Also you have alot of toxic unstable ppl with really bad comps and connections. Once you get past that those hinderances become less apperant and skill level and RNG plays more of a role.
good luck getting out of your ELO hell....