Remember Dota is a game comprised of many different skill sets. Until you approach pro-level skill, almost no one brings the same capacity in all skill sets, and we still compare pros to each other and recognize the subtle differences in different game aspects. Additionally, while people do not admit this, every single hero that you play would have a different hero specific mmr if the system tracked that. Players who never play support and reach 4k on cores, do not pick supports and play a 4k supporting role, they will lose, say they can't win with support and go back to playing cores. This goes for any hero/role that is different than what you have primarily played.
I'm not great at Dota, but if I used your steam account, I would win almost 100% of my games until it reached 3.5kmmr. I can say that with almost 100% confidence. Its up to you to believe this is true. I would lose some games, perhaps against players who were harder smurfs than I would be, but the climb would be dramatic. There is no intrinsic force holding your account down. Remember there are 9 idiots in your games, because you are not an idiot, the opposing team has one more dumbass than yours. That matters over time.
People mentioned that leadership, mechanical superiority, greater action efficiency, better item builds tailored to game needs, and we can also add map awareness, multi-unit control, map manipulation (stacking and pulling), and most importantly map manipulation to enable objective taking. Every player you play with including yourself will have different ratings in all these categories. One game you might get 4 allies who have no leadership ability and do not listen, in such a game your leadership calls will not win you the game, but your mechanics might. But lets say the next game there is 4 people who want to coordinate and listen, in a game like this leadership may be the deciding factor in the win.
The same type of situation can be constructed for any combination of Dota skillsets. Lets say you have an ally that never looks at the minimap, relying on them to counter TP a dive you see coming is a poor way to win. If you understand that your ally doesn't have a skillset, don't risk winning the game on that skillset. Your ally should TP in lets say, but if they do not what should you do? Yell at them? Ask them in hindsight why they didn't TP? Stay at the tower until you die, feeling justified in your decision because it was the "right" play? One of the worst things people do, is to turn a mistake by a teammate into a mistake by the team. In my example above, if you stick around and die when you ally never assists you that's making it a team mistake. The right play in that situation is to leave the tower yourself, find some safe farm or xp, but the worst thing you can do is get yourself killed and feel justified in that because your ally should have reinforced you but did not.
The only way to improve at Dota is to hold yourself accountable to the things you can control. Low tier dota trends into games where they last for an hour, everyone still only has 2-3 maybe 4 items. People randomly die with minute long death timers and eventually one team loses a rax because of random events lining up. Don't let games turn into this. Implore your team to finish buildings before they dive. It won't always work, but if they listen it will win you games.
I can first person coach you in a game if that interests you, we can at least dialog about what I see and you can have a frame. I've done that for Cyni and Intrinsic from time to time among others.
