Sure, Butler is a better player now, but he'll be 28 years old, has a balky knee, and makes $17.5M a year (with with an additional $58M owed through 2020).I can't tell if you're overrating Saric, or underrating Butler. I guess probably both?
Saric is 22 years old, has no injury history, makes $2.3M this year and is cost controlled through 2021. Saric is also taller and a better rebounder.
As Saric's age, Butler was playing 8 minutes a game and averaging 2.6 ppg. In my view, unless Butler brings you a championship this year or next, Saric is a more valuable long-term investment.