Большие преимущества ... доказано или доказаны

It's only a grammatical question. I see in a translation in a grammar:
Большие преимущества крупных электростанций и обьединённых электргических систем доказано развитием наиболее могучих стран мира.
Большие преимущества ... доказано или доказаны ? Of course доказано refers not to
преимущества but to the subject as a whole. Apart from the case of a subjet verb "Читать было интересно" where there is no other solution, when this anomalous concordance in gender is accepted? Thank you.

It should be доказаны. Otherwise the sentence sounds just wrong. And the verb DOES refer to преимущества here.

Thank you.