A center's job is to anchor the dialogue to the screen. A soundbar is the wrong tool for that job. It's designed to distribute sound, not "center" it. All those drivers on a soundbar (terminology note: tweeters are drivers, too) are necessary because of the complicated job that a soundbar has to do, not because more drivers = better sound.
Also, the center needs to match the L and R speakers in timbre, the more closely the better. The soundbar is likely to sound very different from your L and R mains.
This is definitely a case of trying to fit a square peg into a circular slot.