is doubting myself the reason im not consistent?

so, this has been a thing for me for the entire 6 years ive played, i seemed to be a much better player in seasons 2 and 3 than i am now, granted i i mostly played normals and only played a few champions i just seemed better overall not really sure why, for example in mid season 2 i somehow managed to 1v5 and get a quadra kill as singed i was able to last hit a lot better and was far more consistent with my play, although i didnt have the game knowledge i do now, fastforward to now and i am still bronze 5 i tilted a few months ago really badly and was on a huge losing streak and made a bunch of mistakes dropping to mmr, which to be honest i didnt even know was possible, an old friend of mine used to duo with me and we would play customs together tto relax at times and he would almost alwasy beat me, he was silver 3 at the time or silver 5 or something, i would always say that there is a reason he is silver and i am bronze and that is because i suck, he would respond with you dont suck you taught me a lot of what i know about the game you just need to work on mechanics and last hitting, so my question is, is my mindset what is holding me back? because sometimes i seem to be able to throw my caustion to the wind and just not care and do really well and be on a winstreak then at some point i go on tilt and make a bunch of mistakes, hard im not sure what causes this any ideas?

sorry for the wall of text