Of course not. You can MT Vohu with the next MT in April.
If you want to improve water you can get Cthulhu now. However she will be more usefull in 9 months with her AW. Maybe you will get her till then.
Otherwise you should maybe work on your thunder team because of elemental disadvantage.
Therefore get Baal U imo.
Honestly, I feel like overall usefulness would be SSR Nike (AoE heal, AoE buff, debuff), then Aphrodite (AoE heal, AoE cleanse, AoE combo buff), then Saraswati (single target for everything, only really shines in burst builds).
But that's just me. I like getting the most milage out of my kami and the more often they're likely to do something, the more value I'd give them.
This can even extend to when the meta will shift for a team, cause eventually there can be kami that will replace previous ones in terms of value.
Shade on KH, fire main.
Wind Rag farming team:
Well, currently you want this water SSR for later:
Shiva, Cthulhu, Poseidon, Sarsawati, Asherah and Snow Raphael (only for off-ele if you need dmg cut, otherwise no need for her)
Aphrodite isn't bad but Sarsawati just has the better synergy with Vohu later.
Therefore I wouldn't MT her!
Isn't Nike not already phased out of the meta?
I mean the current ideal water Burst build is: Sarsawati, Asherah, Cthulhu and Ryu-Oh/Snow Rapheal + Shingen with SS/Ambush.
Tbh I find her DMG Cut + Orb eat way more useful then what Nike U does.
Furthermore with Herc you don't need that many debuffers anymore. I would run if you can... Ashy, Shiva, Ryu-Oh & Cthulhu/Snow Raphael + Herc with PF
The problem with Saraswati is that she's 100% worthless if you don't have Vohu. That means you're buying a Hime now which will be useless for the next... four months, until the next Miracle Ticket? And then you can ONLY buy Vohu or you're fucked, basically. So you'll this MT entirely if you want to get something for some other element.
So, I certainly wouldn't recommend Saraswati either.