This achievement description is outdated as of March 7, 2018. It actually pops by unlocking 60 Talents. I haven't unlocked it yet on Steam but I got it on Xbox One using the old method and I struggled to find a definitive answer to how this unlocks in 2020. You can obtain this now by unlocking 60 Talents other than the ones you start out with. A Talent is unlocked when a champion reaches Mastery Levels 2 and 8. This means one way of looking at it would be to have 30 champions reach Mastery Level 8. Currently the game has 45 champions so there are plenty of ways to approach this.