Even if there was a Geonosian whose only ability was to hit for 1 damage you would still use them for this team so long as they had a sufficient amount of health and/or protection.
Each Geonosian is going to call all other Geonosians to assist, and each Geonosian is going to add their hp/protection to the group pool. Every Geonosian acts as a force multiplier for every other Geonosian. The only time you should consider dropping one is if they somehow add a sixth Geonosian character and you're debating who the odd bug out is.