One daily power, some encounter powers, warlord support, and most of the team is strikers. At level standards, and fewer of them than the party, arent hard to take down in 1 round.
Not that it matters if it's 1 round or 2.
Well, it does, doesn't it? If it's two, the archers ring the alarm! Even if it's one, the whole party still has to make their stealth check AND win initiative to launch the 10 or so attacks that are required to take 3 monsters down before any one starts its turn... and rings the alarm.
(Also, due to damage vs. hp scaling, this stops working at mid-parangon levels.)
So I gather the PCs are basically alpha-striking. But that ought to be a very minor encounter, because pitting 3 low-level monsters vs. 5 PC (in a single wave, even without a rest afterward) is MUCH easier than 5 at-level monsters.
So maybe the challenge for the players is to prevent the monsters from regrouping. If the player do this, and alpha-strike each sub-group, they will prevail. If they don't the monsters regroup and they'll be toast.
But that makes protracted fights something they will have to avoid at all costs. This, in turn, disqualifies pretty much every power except damage-dealing. Defensive powers, in-combat healing, and very notably, defenders (marking a creature that's dead in two turn is pointless) and control (save ends and action forbiddance is useless if they're already dead) are useless.
It's not too surprising that all your PCs are strikers and -I presume- a taclord!
Is this really what D&D4 was designed for? Games with a simpler combat model, and long-term attrition, such as OD&D, would seem much more appropriate?