If they are stuck in Silver or Bronze let them be. They will just feed in gold even more. I assume that their mmr got higher after the boost so they could get a lot better opponents. But yeah I got to say Platinum sucks too. I had a top lane opponent who was Platinum and he missed a lot of creeps and took free harass.
I currently ave a 80% win rate with Jayce from 28 games. After I finish leveling up my smurf I'll try not to lose with him at all. I've been watching some streams where players get a 100% or 90% win streak from 20+ games. It could be possible as I started playing ranked when I had no clue what I was doing and lost like 3 games with Jayce. But it's a long way ahead.