"NOT TERRIBLE"??
Is that a comforting diagnosis?
Very few of us do the machine method where you change it all out i.e. running a pump and replacing the total volume in a closed loop.
Doing the simple drain, yes you will leave some of the old ATF fluid in there but if done correctly, you will not be overfilling it since you will be only replacing as much as you take out, roughly 4+ quarts.
Think of it this way, when you exhale, you do not completely empty your lungs of the "old" air and on the next breath, you only inhale as much as you exhaled. You don't over-inhale and explode (if done properly).
Get it? The remaining "old" air over successive breaths gradually mixes with the new air and you keep on living.
I have 200K on my 2005 and 140K on my 2008 Outbacks and do the simple maintenance like oil and transmission fluid changes myself. I've heard too many horror stories of fast service shops mistakenly draining the transmission and then overfilling the oil!
Good thing is that, as you report, it has been dealer serviced so they likely had more done than what was needed to be done and the car is likely in good shape for now. I cringe when I sit at the dealer and listen to the hard sell to unsuspecting customers.
You probably can get a history of the maintenance if you know the dealer used and go from there.
All that being said, there are many here who are pros, some with real shops, and others like myself that would rather do the simple things and know they were done right instead of sitting at a dealer for hours on end waiting for them to change the blinker fluid and charge me through the nose for the privilege.
Depending on where you live in Bklyn, you may not have the luxury of being able to work on your car but if you do, it isn't that difficult to do the simple stuff.
Capeesh?