you can just make a deepone mage it hurts your passive scu alittle but it also means you always have a weapon and a free restraint escape all of the seawitch abilities except the fog scale on wis anyways

I would say, you main source of damages are still Juicing and Summon Siren. Not the Water Shot. You can still put all your WIS and focus on dealing damage with Water Shot  but it would be better to rebirth to other race and use Water Staff instead. 

Juicing is main damage source of succubus build. If you have high Weak status, most of the male enemies will try to grab you instead of attack you. You will have a gap to grab them by using Juicing skill instead. Once you are in sex whether entering it by you grab the enemy or they grab you, you can use ASDF key to deal damage depends on you are using which hole to sex and the sex attack will consume your Stamina. Sometime it will exit the sex and stun your enemy a very long time, it will allow you to rest to recovery your stamina and allow you to grab them again until they are dead. It is suggest that you should grab the enemy instead of let them grab you since they will injured you if the sex is started by letting the enemy to grab you. In this way you are impossible to lose if you still have stamina and the sex is not interfered. Please note that your Siren will interfere your sex battle and the enemy will be angry once you are perform any type of attack, including grab them by Juicing and stun them by Idol of the Believer although they are not dealing any damage.

In normal form , you will need to wear the armor which can increase Weak. Sex doll set is very good for increasing you DEF and Weak at the same time. If you are planning to use other type of armor like Martyr's Set, then Glass and Atoner's Pendent are very good equipment for you to increase Weak. In Sea Witch form, it automatically give you 1000 Weak so you don't need to worry about the armor.

Summon Siren is the other way to fight which allows you to deal with multiple enemies and the enemies which cannot be juiced. Siren only deal 1 hp damage but they are also dealing decent Stamina damage which depends on your WIS. You can consider that unit in this game has two type of HP bar: The actual HP and Stamina . Either one go to zero will able to defeat the enemy. You can have 2 Siren at the same time so just spam summon it when it is defeated (You can kill it by approaching them and press confirm button or just use your water shot to attack them when they are no Stamina to fight and enemy is focusing on attack you). It is better you use "Rallying Trumpet" which allow you to command them to move and encounter enemy so Lona didn't need to move too close to the enemy. They should be able to dealing with most of the enemies. Some enemies may be too strong for the Siren like Big Mama or DICC the Impaler. Bring some Frag Mine and use them instead. 

The Wiki page also told you Water Shot wouldn't be your main source of damage. Only use it to draw the enemy if you needed and let the Siren do the rest of the job. It also make enemy angry and target you if you attack them until they are attacked by the others. So only use this skill if you are not planning to juice your enemy and make sure your Sirens are still able to attack your enemies.