Okay, so let's say that Saraswati has sped up two Hime. I mean, one of those abilities is going to do nothing (or next to nothing) half the time, but hey.
Now what?
You're still waiting for the last Hime. What exactly did you accomplish?
In other words, bringing another Hime with a different skillset is simply going to benefit you more than a Hime who will do nothing for your team.
I'd also like to add that there's more to this game than just how fast you can Full Burst. Yes, that's certainly a direction we are heading towards (at least until they inflate the numbers so much that that alone won't cut it anymore), but we're not quite there yet. And we won't be for a long, long time. Even when we ARE there, only omega whales will be able to do it on multiple elements.You should probably try her, since Belphegor makes Rage bars a complete joke. Note that there is only Hime who is equally good at reducing Rage bars - Chemobog (at least until August 2018, I haven't checked the last four months). Most of those Rage bar reduction abilities are quite weak, but Belphegor's is just insane.
Of course, you can be at a point in the game where you can Full Burst Rage bars entirely out. This has very much been a thing since PF, after all. But if you ever find yourself struggling, just bring Water and use the SSR quality SR.Are they powerful? Since 2/5 members having 50% damage cut against one element (Fire) only doesn't sound very powerful to me. SSR quality is generally bringing 30% (Snow Raph, Raiko, Pluto) or 40% damage cuts (Raiko, Karin, Gaia, Water Osiris) against ALL elements, to ALL party members.
And what good is it going to do to shield two party members? Or rather, one plus Saraswati. If it's AoE, you're going to get badly hurt. If it's single target, you're taking a big gamble without Kushinada, or a small gamble with Water Osiris.
That leaves her with:
35% Elem+ buff which would be impressive... if it was the full team. For the record, on Full Burst, that's about 14% Elem+ buff teamwide. SRs generally buff for 15%, and SSRs for 15% or 20%. So it's decent, but certainly not powerful without synergies.
Her heal and +25 Burst. Decent, but again, two out of five targets. And +25 Burst on 6 turn CD, for two members, is... 8 Burst/t. SR quality is about 10 Burst to all on 8 CD so 6.25 Burst/t, and SSR quality is around 20 Burst to all on 8 CD so 12.5 Burst/t. Two notes though: the "quality" is all over the place in this stat, and maths doesn't entirely cut it here thanks to Bursts feeding +10 Burst to all below. Overall, this is the buff that makes or breaks Saraswati.
Finally there's the Combo+ buff (30% Double, 20% Triple). This increases the amount of hits/t from 1.14 to 1.84 for three turns for two people, and with the cooldown it's to 1.49 hits/t on average. For comparison, Herc runs at 1.64 (but will gain 19.91 Burst/t due to his buff during, so is still faster than Saraswati buffed targets) and on average 1.5 hits/t. This would be really broken if it was teamwide, but again... it just isn't. As it is? It's decent.
Not a single one of Saraswati's abilities scream powerful to me. At all. If you have Vohu, that will basically solve Saraswati's problems - there now is a member in the party who is actually fast and thus the fourth party member won't bottleneck you anyway (assuming that the Combo+ actually does something, which will remain an issue until Tiara set bonus). Or if you want to tank, Water Osiris actually compliments Saraswati quite well (which was news to me). Without either of those? ... yeah, I'm still saying that Saraswati belongs in the trash bin.