This isn't a huge jump in talent at the point guard, essentially swapping out Sessions for Augustin, but Sessions does have the advantage in most statistical aspects. He's a better scorer, especially closer to the rim. Sessions' last season was surprisingly good from three, hitting 44.3 percent of his attempts, after he didn't even attempt 40 in a single season before this year. Whether his range is finally coming around or if last year was an outlier, I guess we'll see. But if he has the form, mechanics and repetition, it's possible he could be a good shooter as well as a slasher. His stats improve if you look at his splits as a starter, too (14.4 ppg, 7.2 apg).
Augustin did outperform him as a passer, however. Augustin had a 38.9% AST% (percentage of FGM he assisted while on the floor) while Sessions had 35.5%. So it's close.
Personally, I like the signing. It's not a big salary increase over what they could have paid Augustin for better talent.