I've found I have a decent amount of impact. Mostly because I make a somewhat sensible pick instead of "lET's gO VaYnE!!!"
You'd be surprised at the impact you can have based on your pick alone. For example, you can make it so your team is remotely able to do anything in late-game by picking a durable champion.
Also, I'm pretty sure Trinity is still more popular in general than IBG. Like, Nasus is going Trinity right now instead of IBG even into AD lanes.
One of the issues for a lot of lower tier is that they think they can stay toplane for the entire thing and make an impact. The thing is...You can't do that. You need to be looking at the map and trying to figure out what impact you can make as soon as you have the bare minimum you need to function. You have a lot of opportunity to hurt the enemy jungler, especially since they can rarely hurt you enough. Go invade and steal their buff or crab or gromp or whatever. Go take something easy enough to take then get back out. Look for times you can roam mid. See if you can make a TP play bot.
And even if you're a splitpusher champion, try to teamfight around mid-game anyways. Odds are you're the strongest turret taker, since you most likely either have trinity+AA reset, or Demolish, so you can at least help there. And in mid-game you're generally too durable to be killed easily by an ADC while you likely out-damage them. Transition to a splitpusher later, sure, but at the start you need to be looking for ways you can help the team.