Isn't this why we have a DM instead of a computer running the game?
Depending on the group composition, equipment, individuals, etc, you tweak the encounters to be an appropriate challenge.
In a recent delve, we fought a red dragon, that the DM had tweaked to have 3 initiatives (losing 1 initiative when bloodied). It mopped the floor with us (though we did take it down to where it only had 41 out of 300 or so hit points), but I was playing with some inexperienced players. Later a more experienced group took the dragon down with 3 or so casualties. I think an experienced group who knew how to use the characters, got their action points off quickly taking the dragon down to bloodied, would have beaten the dragon with maybe 1-2 casualties. (Being a delve at a Con, the encounter was designed to be especially lethal of course.)
The DM is always free to make adjustments for a more fun experience, for both sides of the table. In my games, I always take party power into account (from equipment to player experience) when designing encounters. I might use more lower level monsters, I might increase damage, I might lower defenses on higher level monsters, or increase defenses/add tough on minions, I might add minor/immediate/free actions to elites and solos. I play with a DM who likes to add action points to a few standard creatures, or maybe add a second action point to an elite. It's all a matter of finding that balance of where an encounter is appropriately challenging and fun. There isn't a single right answer.