What is the reason that makes some matches end up one sided, even in pro gameplay i see that happen sometimes. I am pretty sure it is not(but maybe sometimes in solo q or comp in general) because of mechanics. But what is the reason behind...

I'm not sure how to say this but whenever I use the classic gun it feels like I'm shooting noodles at the enemy. it feels so loose and it feels like it's shooting around the enemy, this is the only gun I have a problem with, any tips?