The only way signing Mac makes sense is if Gattis is used in a trade to fix 2B (I agree with wholeheartedly) or to bring in an Ace (I don't agree with). At that point signing Mac is almost mandatory.
Teams like the Braves have to be smart about allocating their resources. It is not smart to spend 10%-15% of the payroll on a position where you can get comparable production for peanuts. So use that money to fix 2B where the production is less than zero.
No faith in LaStella? I wouldn't trade such a valueable piece when we might have an in house replacement that is at least worth trying out. If you want to hedge that risk with a one year deal to someone like Kelly Johnson then fine but to trade such a valueable piece like Gattis doesn't make much sense to me.