Sure, but what's the point of having extra cores if you don't use them?
My point is not that you cannot keep 4 cores somewhat busy. My point is that you can rarely get a linear speedup from parallelization, so 4 cores will in general not at all be 4 times as fast as 1 core or twice as fast as 2 cores.
Your original statement was still misleading. You said it'll use more power but you only get more performance in some cases. Strongly implying that you always use more power. You didn't say anything about the ratio of increased performance to increased power consumption.
You rarely get a linear speedup from parallelization, but that doesn't mean that the sub-ideal scaling is all lost in redundant work. If a core is waiting for another core to finish something it can be clock gated or possibly even power gated. In some systems its voltage can be dropped independently. The point is, it's more complex than saying distributing a task to N cores will use N times the power no matter what the performance scaling is.
On the flip side, distributing a task to more cores can use less power if the clock speed is lower. If you cut the clock speed in half you will generally use a lot less than half the power, at least if you were anywhere near the higher end of the clock range. This can work asynchronously to an extent. If you have one task that needs 1GHz and another that needs 0.7GHz it can be better to execute them on two cores at 1GHz, clock gating one of them some of the time, than one at 1.7GHz. This is especially true if the SoC needs especially heroic voltage scaling to hit their higher clock levels, as many SoCs these days have (Cortex-A15 was never really intended to go past 1.5GHz in phones)
(but I doubt ED will be open to large change on the project)
