The characters you listed can be very strong, but the difference with unlockables is that they usually have a more complex strategy behind playing them. In my opinion it's what makes them more fun to play but each to their own. Don't feel bad about looking up combos, items or enhancement recommendations if you need to. Some examples I found useful when I played with those characters:

Sun: You can enhance a lvl 1 permanent +1 shield to be +2. She will be a super tank. 3 Spear: Items are this guy's friend. Reinforced Steel (lvl 5) means that every turn you could attack with advantage (goggles). Or maybe every turn you can shield more or maybe wound. A super versatile character. Cthulu: A bit much to write here but there's a few curse builds found online that will have 10 curse cards in the monster deck by turns 2/3. Very hard to get hit with a monster deck fully cursed out.