How is Arjuna?

All 5 star servants are heavyweights in their respective classes, regardless of the tier lists online, meaning that they are absolutely viable. You can run "crap" SSRs like Saber Altria and Arjuna and be just fine for a majority of the content in FGO. The problem of valuing servants arrives when you start comparing these servants within the SSR or even SR category. Take comparing Gilgamesh to Arjuna: one is the nuts while the other is mediocre compared side by side. Another problem is whether you have a team fit for Arjuna or not. Do you have an Arts/Quick team ready for him? Play with what you have, not for a meta you can't reach just yet.

Well, many people will tell you to focus on Robin & Euryale for Camelot, not Arjuna.

Euryale is very useful against male Berserkers & Sabers (and they are a lot in Camelot apparently) and Robin is the king of ST NP against them.

Arjuna has a higher stats and you need a team built around him to make him viable.

I think He's worth using for general purpose. His deck is kinda weird (thus no NPBB for maximum damage with his Buster Burst). Tho, He'll outdamage your low stars in general damage. Robin, Euryale, David are great low star Archer because they have their own niche that Arjuna doesn't have, so there's that. If you can, just raise them all.

if he is your only SSR (just like in my case), its worth to raise him for a little bit more damage from your team, and for farming