The issue of smurfs has little to do with them allowing alternate accounts and far more to do with keeping a consistent flow of content to keep people entertained along with a ladder system that doesn’t forever reset you to within a couple hundred rank score of where you were at the start of the season.
Smurf’s Primarily happen because people have nothing new to do or explore. So they create their own fun by creating new accounts to “grind” up and earn achievements again.
As someone who has alternate accounts myself the main reason I have five other accounts is so I can go for the achievements again.
For the short term, the release of OW2 will see a severe drop in smurfs. Whether or not it remains that way is entirely up to Blizzard to keep their game interesting and fresh.