Descent and balance

Descent's a great game, but our group's reaching the point where the Heroes are rapidly outclassing the Overlord player. We're only 4 or so missions in, so hopefully the balance will be shifted in the later missions.

Two of us took four heroes against the forces of darkness this week, and won by a margin of over a dozen conquest tokens!

We only used pretty basic strategies too:

* Open doors at the start of a turn, run in and collect chests/glyphs before slaughtering minions before they can react.

* Quaff fatigue potions with gay abandon to achieve the above - spend all money in ton on more fatigue potions!

* Position heroes to limit the areas the overlord can spawn in, as (s)he has to spawn out of LOS.

Now, either there're some equally basic Overlord tactics we're missing, or the game's balance is crazy... My thoughts on addressing this imbalance are:

* Start the heroes on zero conquest (or one, maybe) as the chances of getting slotted before activating a glyph are slim to none?

* Allow the Overlord to play multiple spawns when the boss room door has been opened - after all, the remaining minions would rush to the defence of their master, right?

* Give players fewer skills - maybe draw three as standard, but discard one?

* Maybe we should have just had one hero each, instead of two?

Any thoughts, or (better) advice? I'm aware that the expansions swing the balance back the other way, but we're only playing vanilla descent for now!