Just rolled and got trash

All servants are eventually workable especially with a good support like Waver, but ooft those are some really cruel rolls. I'd suggest you actually save up resources for your other existing servants, even most of the 1-3* ones can outclass both of them.

Despite being a meme, Stheno is at least somewhat worth more leveling compared to Fione, but only for the really niche role of stunlocking males, which can be handy on some boss fights.

Otherwise though it is better save up unless you literally don't have anything else to spend on, and if you are going to spend on it, Stheno will serve you better than Fione, since Fione literally don't have much upsides, and Stheno has a (albeit inconsistent and unreliable) niche.

If you are in need of arts lancer, raise Fionn. If you need male charmer along with Euryale, raise Stheno. Otherwise, don't waste your resources for them in the meantime.

I'm a day 1 ftp player. I saved almost every SQ for Jack [Did 2 10 rolls], and every ticket, rolled everything in her first banner, got nothing remarkable. Stop whining about not rolling SSR in every 10 roll that you pull, most of the welfare servants [Nobu, Santa rider, Kintoki rider, Shiki Assasin, Elizabeth Caster] [And some 2 or 3 stars servants] are pretty solid [Hans, recular Cu, Mash]. Regular Cu is one of the best servants despite being 3 stars. And you had a free 4 Stars servant to choose like 2 weeks ago, yes, it was a pretty limited choice but you had it for free.