It depends on the champion - some really need books to function well, others don't. But even champions that need books may still be ok and worth using while you wait to obtain the books. 

Which epic champ(s) were you thinking of if I may ask?

I have fang cleric, necrohunter, sandlashed survivor, shaman, jizoh, warden, masked fearmonger and high Shaun.

Fang Cleric, Necrohunter, Masked Fearmonger, Shaman, Warden and Jizoh are not woth to invest books anyway. You will find better champions.

"High Shaun" is probably the High Khatun. She is a very usefull champ and doesn't need books. You could use as many books until her skill "Rally the Horde" got his cooldown, but you could play her even without any books. She gives a speed aura and her best move is to use the mentioned skill to get a speedbuff for your team at the beginning of the battle. She can do that without reading books.

Sandlashed Survivor is a really good champ and woth your books.

Here is a List ,, It is a good ROUGH Guide to follow ,,,, 

https://ayumilove.net/raid-shadow-legends-list-of-champions-by-ranking/

Thanks guys, very useful tips. I appreciate it.

Sandlashed survivor can definitely do some work. I highly recommend building her!

Very useful the list, especially for those, like me, that I am amazed by this game!! It was about 2 years I was playing State of Survival and I was satisfied but I was playing also other games. Something was missing. Then I thought that the designer or designers had planned every move so they "knew" in some way, what I would do in a given situation. I wrote a doctrine thinking a lot about that, because I am a Player. And I want to be a good player. Not for the approval of others, but for me. Can I exercise something I learn as the experience grows in the game in my " every day life" ?

So I am here playiing as much I can!🙂 To see my heroes win an entire arena!!😁

I am in a greek clan, I am greek too. But in the clan noone communicates. I understand it but I feel that is essential, if you look forward better. 

So thank you for the guide and I am glad I am here. Love Is The Answer!