With the exception of war, you dont need tons of heroes to raid or even on titans.
A couple of 4* and 5* would still do fine.
I have over 30 5* heroes but only 10 of are ascended to the max. I have to gather AMs again for those.
If you ask me, for 5* if you have 2x decent heroes for each color is already sufficient.
Quintus is good if you know how to use him. Thorne is an exception. Bad hero that he has no special skill nor high damage. He needs to be flanked by 2 very good heroes and preferably red. He is still viable if you really have no other choice (maybe F2P). He is a pure old school tank with heavy D and nothing else. I have recently played against someone with a Thorne tank recently and flanked by 2 GMs. Took me 3 tries to win.
Conclusion: new players need more heroes; veteran players need more AMs