My creative brain started working on a solution to the lack of balance among the spheres in solo play (it is my personal belief based on extensive play of this game that decks without threat reduction and quest power cannot win on their own. Particularly, Tactics sphere cards are heavily designed as support cards (and not just the ones with the "ranged" keyword, either). After some thought, I came up with these 5 cards that I think could do wonders for balancing the weaker spheres better. It sucks knowing half of all the cards I open just set in the box unusable.
Here we go…
1. The Last Alliance cost 1 Tactics Event
Play only during the planning phase. Reduce your threat by 2 for each ally card you play this phase.
This plays into one of the few strengths of the Tactics sphere - the ability to collect a great number of resource tokens while you wait for the right moment to play specific cards. You can drop a whole handful of cheap allies on a single turn and reduce your threat to a manageable level.
2. Council Summons cost 5 Neutral Event
Search your deck and discard pile for any 3 ally cards with different names and put them into play with 2 progress tokens on them. Those allies cannot quest, attack, or defend while they have progress tokens on them. During the refresh phase, you may move 1 progress token onto any location.
This would allow you to mix up the spheres a little more than is currently possible without "mana fixing."
3. Arwen Undomiel 6 Threat Hero Leadership
3 Willpower/ 0 Attack/ 2 Defense
Arwen Undomiel can't be chosen as one of your starting heroes and is instead shuffled into the player deck at the start of the game. Raise your threat by 6 minus the number of players to play this card from your hand. Resource tokens from characters you control may be spent as though they were of any sphere.
Very powerful, but the tradeoff is you have to actually draw her and then raise your threat. Her threat is the lowest in the game and she can quest. She also provides mana fixing.
4. The Art of War t cost 2 Tactics Attachment
Restricted. Attach only to a Tactics hero. Whenever a character you control participates in an attack that destroys an enemy, place 1 progress token on the current quest and reduce your threat by 1.
This one should be self-explanatory. If combat is the flavor of the Tactics sphere, then it should directly tie into the win condition of the game.
5. Fearless Leadership cost 4 Attachment Tactics
Characters with the Ranged keyword may attack enemies in the staging area at +2 attack.
So there you have it. With those 5 cards, I think the game could come a long way in allowing each sphere to be equally playable in solo while still retaining individual flavor.