The is indeed LP decay with time, but maybe your rank isn't high enough to do it? I see it in plat.

But really I was talking about how MMR gains decay with the number of games played, not with time.

You don't seem to really grasp anything of what I wrote, do you? Clearly you cannot get stuck forever where you don't belong. But it takes a much longer time to climb at low ranks than it does at high ranks.

You don't really seem to get the theory but go ahead and just try it, start an account and climb from bronze (Iron now I guess? Never had a smurf that low) to plat. The games at very low elo will sometimes be a lot harder to win, even if you stomp lane because there's a lot more smurfs/throwers in bronze than in gold.