True to some extent, but insulated oven will get hot enough on reduced power but won't warm up as quickly. Reason behind project is that the mains circuit that has the oven on, has several other large current devices that can't simply be de-rated. Hence when the these other large current devices are on the maximum oven power consumption is reduced as it would overload the mains circuit.
And yes I wish the mains circuit could be uprated but this is out of our control 