Understanding how to use a lead to close out the game is what prevents innumerable silvers from actually making it all the way through gold and into platinum.
With that said, I have two big things which I do.
1: Phrase it right. "Don't get arrogant" is kind of.. negative, for lack of a better term. It's putting your team mates in the context of "can't", rather than "can". We, as people, do not like being told what we cannot do; this amplifies when it comes to strangers on the internet trying to control our leisure activities.
When I find myself in your situation I personally say "We have a lead, play to win before the lategame.". Where as your words can tap into negative emotions of being controlled, mine is acknowledging their lead (and therefor skill), and trying to direct their focus. It's a subtle difference, and it doesn't matter to everyone, but I've noticed it can help.
2: Looking through your games, I see you play mostly damage. Even going so far as to build your xin and j4 basically as glass. This isn't bad, and in fact works fairly well, but it comes with a problem.
You're dependent on other people to start team fights.
You can make picks, you can duel, but once the enemy starts grouping.. Any team fight you start is probably a team fight you die in.
I, personally, have the best success when I'm someone who can successfully force fights, or at least make the enemy choose to fight or give up an objective. In the past I've played a lot of trundle, currently I'm stuck primarily on Sion.
Once the laning phase is over, your team is going to (generally) naturally gravitate towards their front line. The default hierarchy of pub games is that the tank player tends to be the one who calls the shots and makes the decisions, with the rest of the team GENERALLY following suit. Being that player allows you a measure of control over your team, and allows you to force them to close out the game. It's still often times like herding cats, but it's a lot easier to herd tanks as Sion with 3k hp at 20 minutes than as Zed.
