Keep in mind that many of the ideas being thrown out here may hinder smurfing, but any sort of SR anchor has a flip side. You’ll be locking boosted players into a higher SR where they don’t belong, so people just need to buy a boost once (or once per season) and will sit at their rank ruining games for as long as they want.
The proper solution is a combination of machine learning and bans. By manually identifying enough smurfs and feeding in the data, machine learning can be used to identify players who are alternating between sabotaging and carrying games, by looking for factors unique to this behavior. Hire enough people to monitor smurf reports and feed enough data to a machine learning algorithm, and you can automatically detect this behavior in a short enough time period to make it a relative non-issue.
Nothing will guarantee you never face a smurf, but if someone only gets 20-30 games out of a smurf account they’re going to hesitate to keep buying new games and leveling to 25 to cheat the system. Right now, they’re getting hundreds or even thousands of games before anything happens.