Grid-scale transformers are very efficient. The tiny pole-mounted ones used in the US and some other countries probably not so much, but everything north of 50-100 kVA gets into 99+ % efficiency.
Just because generator/machine set transformers and 380/220 kV step transformers require semi-active cooling doesn't mean they're inefficient... just means that they handle a huge amount of power (MWs), so even at very high efficiencies that translates to a lot of heat in absolute terms.
Just because generator/machine set transformers and 380/220 kV step transformers require semi-active cooling doesn't mean they're inefficient... just means that they handle a huge amount of power (MWs), so even at very high efficiencies that translates to a lot of heat in absolute terms.