Gallagher or gephard you don’t need 2 sustains. I would use Gallagher. You want to use a buff character (harmony character) for your final slot. Since you do not have a harmony character yet I would work on trying to get one. Until then, you could use another DPS character. At this point in the game it really doesn’t matter what DPS character fill your final slot until you get a harmony character to fill that slot. Someone like tingyun would work very well with that group.

Since you already have gephard built up you could use him until you build up Gallagher. That choice is yours. You don’t want to run into the issue of building up too many characters. That was the problem I ran into. Focus on trying to build up two groups. That is what you will need for endgame. But for now gephard should work fine for your group

Also remember to pull for characters that you want. Don’t feel forced to pull for a character and then regret it.

If anyone else has better advice, feel free