Sort of. But as you start hitting the minions, their damage capability goes down, while en equal-level standard monster will be able to keep murderizing just as well until he goes down.
This is only true if the PC(s) attacking the minions have anti-minion powers and even then it can be pretty questionable.
A single brute or soldier against a PC Cleric is less threatening than 4 minions against a PC Cleric, even though they can be the same XP.
Both tend to have the same chance to hit (for simplicity, let's say 50%, but it is usually higher for both versus a Cleric). Let's also say that the Cleric has a 50% chance to hit the enemies.
Minion Combat:
Round one: 2 hits on Cleric. 1/2 hit on Minions (let's be generous and say that the Cleric hits).
Round two: 1.5 hits on Cleric. 1/2 hit on Minions.
Round three: 1.5 hits on Cleric. 1/2 hit on Minions (another minion falls).
Round four: 1 hit on Cleric. 1/2 hit on Minions.
Round five: 1 hit on Cleric. 1/2 hit on Minions (another minion falls).
Round six: 0.5 hit on Cleric. 1/2 hit on Minions.
Round seven: 0.5 hit on Cleric. 1/2 hit on Minions (last minion falls).
So, the Cleric won in 7 rounds (instead of 8, but I had minions attack before they died in the same round, so it should be a wash). The Cleric got hit 8 times.
Soldier Combat:
Round one: 0.5 hits on Cleric. 1/2 hit on Soldier.
Round two: 0.5 hits on Cleric. 1/2 hit on Soldier.
Round three: 0.5 hits on Cleric. 1/2 hit on Soldier.
Round four: 0.5 hits on Cleric. 1/2 hit on Soldier.
Round five: 0.5 hits on Cleric. 1/2 hit on Soldier.
Round six: 0.5 hits on Cleric. 1/2 hit on Soldier.
Round seven: 0.5 hits on Cleric. 1/2 hit on Soldier.
Again, the Cleric won in 7 (or 8) rounds. The Cleric got hit 3.5 (or even 4) times. The damage was greater than the individual minion damage, but it was not twice as much. The single solider also could not flank in order to increase the chance to hit.
All in all, 4 minions are often more deadly than a single brute or solider counterpart unless the PCs have damaging AoEs or other anti-minion powers.
Like all versions of DND, numbers matter. Well used minions can be devastating. For example, minions that attack PC non-Defenders are often more effective then just attacking the PC Defender. On the other hand, 4 minions can often be taken out with 2 or 3 back to back AoE attacks. It depends a lot on party makeup and situation.