I think I agree with most of what is said here, especially what @Guvnor said about tc20 – I have had one tc20 running a long time, and it has never yielded a 5* hero (I honestly cannot recall a 4* either, but I won’t stake my life on that). With one 5* from a tc, I think you’re already lucky. So, work with what you have.
I would say that I love Marjana. There may be better 5* reds, but I think she can make a case for herself as the best vanilla 5* red.
I don’t have Magni, but would like his speed in attack. I do have Richard and Isarnia, but not maxed. For reasons that may not be the best, I opted to promote Frida and King Arthur. If I had had Magni, I would have maxed him, for sure.
In my opinion, none of the vanilla 5* greens are game changers. I have Horghall and Elkanen whom I have maxed out. Still, if I see either of them on the other side, I breath a sigh of relief that they are not Lianna. The greens I really hate to face are Mother North, Gregorion, and Alberich… especially Alberich. Still, you need a green, so if Kadilen is who you have, I would max her out.
I maxed out Joon, and never looked back. He’s great in raids and he is great against titians.
I maxed Hel and Seshat in favor of Sartana, but she’s next if I ever find two more tabards and a tome of tactics.
Let us know what you choose to do.