Yeah, your life is a currency. You can fail 4 times before it's game over. So the time spent trying to get all your Scotts and axes isn't really wasted. Money is the best superpower.
It's just a balancing act of knowing when to stop being greedy while giving yourself a buffer if you run into one of the run ender squads.
I'd say the thief is more efficient than Scott but a lot harder to acquire. HIS upgrades are the ones that REALLY pop off. Like if you get an early thief, then you should just build your entire team around him.
There's a team in the game now where I won by abusing Swampies and a Thief. It's a huge conga line of power and axes.
As far as weak units, I'd like it if you could "evolve" them. Rather than just upgrading a zombaby to be a stronger zombaby, couldn't I have him become a zombie?
Like if I get an imp family member on my team, I obviously should ditch him, regardless of how strong he is, for a critter if one shows up. If my new Critter could consume the previous unit and thus gain his upgrade points and inherent any stat gains he got, if they share the same family line, then upgrades become significantly more worth it.
It adds an element of strategy to the mix.
Also, you could massively buff the summoning decks if there wasn't a cap on the number of units in a battle.
I don't mean letting a player bring infinite guys into a fight. But instead if a unit spawns a guy, that guy isn't wasted if you already have 5 currently alive.
There's some combos that could be seriously nasty if there was a separate summon cap. Perhaps it's something you could buy with cash? If you unlock more "slots" for allies created in battle.
It opens a path for more types of units who have similar abilities. Like a unit who, every 3 rounds, could summon a guy or two.
For players who don't use summons, you could have buyable stuff that takes the place of guys and fits in the same spot. Like siege equipment, or castle walls. The enemy might have to take on your ballista or structure before getting to the dudes.
As far as balance goes right now, it's still a young game. I'll wait to see more combinations and what happens with updates before saying anything about that.
There's a lot of good options here, if you can find them. Part of the strategy in this game, unless you add more ways to guarantee specific units, will be to build a deck based on what's given to you.
After a while a clear meta will form. But I'd rather wait to see what other people do once this game gets a few hundred people who won at it.