Character Card Deck effects

So wait, does that mean with a 120 DB,120NW and 120-199 phantom I'd get the S effect instead of A?

No. What I said was:

The all faction set effects, like all Adventurers, [all] Cygnus, whatever, are based on the highest card, so even if you had one SS Ranked card, it'd give you the full SS Rank set effect

Only the all faction sets, if you have all Adventuers, all Cygnus, all Resistance, all Heroes, the ones that give all stats, are based on the highest card.

unlike the other sets which are based on the lowest card.

With that combination, you'd only get the A effect.

Anyway, while it's nice to avoid damage, I'd rather reduce the damage I take and probably save NX on a few wheels here and there with Luck of Phantom Thief, and Phantom's avoid rate is pretty high already.

Increasing max critical damage, even by 8%, would only bring the average critical damage from (135+150)/2 = 142.5% to (135+158)/2 = 146.5%, an increase of about 3% damage, unless you have actual SE, when the average damage increase would be slightly less than 1%. And that's assuming you crit all the time.

I'm also opting out of using a Phantom card, since it's just meso drop, and not even a sufficient amount.

I wouldn't choose the all thief set, since the set effect isn't that good, and you'd only get an A Rank effect by combining them in that way.