why is it that with Geo ships (and other scattered ships here and there) Tarkin is the best Fleet Commander?
As I understand it, it's the fast start and ability block of Tarkin + the offense bonus for inflicting debuffs + TM jump on 1st special.
But Home1 has abilities that benefit the Geos when attacking out of turn, and they do attack out of turn, so that's not a bad form of synergy either. I haven't actually practiced this with 2 different cap ships of the same pilot gear to check how it really affects winning percentage. Rather, I did not pursue Geos until Malevolence became available because in the early game there was nothing for Geo to do, but many of my Rebels had things for which they needed to be geared up (Thrawn Phoenix & Rogue 1 missions in Hoth TB, CLS was an arena team back then, etc.). Then they introduced Geo TB and the Malevolence at nearly the same time, so there was no real reason for me to experiment with my low-gear Geos under other cap ships.
So I pass on the bit about Tarkin being the best commander for Geos because that's what other people have said, and I haven no reason to disbelieve them.
But if you don't have the gear on Tarkin and if Ackbar is working for you, I wouldn't worry about it. You should do what works for you.