by jrd23
You mentioned that your background is role-playing games. Well, most role-playing games reward players who1. Build characters that are effective in the rules of the game
2. Play with groups of characters with complementary abilities
You don't have to do these, but in most RPGs you will be at a disadvantage (and more likely to lose) if you don't.
LOTR is very much the same. Playing a deck with Aragorn, Legolas and Gimli is like deciding to play D&D with a party of two fighters and a ranger. Sure it's possible, but there are a lot of adventures where you will wish you had a cleric or a wizard along too. This is not a weakness of the D&D design and it's not a weakness of the LOTR design - it's intentional in both cases and makes the games better.
If thematic decks are your thing, why not choose a couple of heroes for theme, and then think about who else they would bring with them to help them on a particular quest, someone who complements their abilities?
For example, you decide to build a hobbit deck based on Frodo and Bilbo (Spirit and Lore). Who would they invite along to help - obviously a strong leader and/or fighter, maybe someone like Gimli or Legolas (Tactics) or Aragorn (Leadership). And these heroes would bring their own followers - perhaps more dwarves (Gimil) or elves (Legolas) or Dunedain (Aragorn). This approack should build decks that have a strong theme and still be capable of succeeding against all but the toughest quests, at least some of the time!