Smurfing is a big issue. The TG ladder in general is a big issue. There have been several big issues since the launch of the game. The devs have tried to fix one, by creating others. The devs dont really seem to care about the multiplayer ladder at all. They much rather add some crappy designed civs to grap some cash instead of fixing the real big issues.
One of these issues is the big mess on the TG ladder. Smurfing is part of the issue. The main root is the elo calculation. The current system promotes smurf account to get more easy opponents and to boost the main account of a user. Analyses of the ratings - Spotting the issues this is a big thread about the elo calculation. It contains multiple possible solution to at least fix the boosting of smurf account and the use of smurf accounts to get weaker opponents. There are some simple options to limit this a lot, but for some reason the devs doesnt seem to care at all.