Was your argument about biomagnification or energy? Because the latter is a less convincing argument: Plants are inefficient energy converters already.
There is nothing less convincing about that. It takes a lot of plants to get some meat. So a little 'inefficient energy converters' are better than a ton of them.
Efficiency of solar conversion is only important in so far as where solar energy is a limiting factor. In our case, it is not. There is plenty solar energy that reaches the earth and that we are not using.