Yes, he's awesome support even at constellation 0. Venti is super good when it comes to grouping up lightweight enemies in Abyss, and with elemental infusion, the damage potential further rises. I'm a constellation 0 venti holder and have never faced any problem in the Abyss. Venti's burst vortex cannot group up heavy enemies; however, when clearing some mobs, he's quite efficient in that role. Also, sometimes you have to protect a monument in some spiral abyss challenges, so Venti can be used there to group up enemies and not let them attack the monument. So, I highly recommend you invest in Venti and level him up as much as you can. Investing in him will pay off in the longer run.