You are correct to a point crushers are often installed for...

You are correct to a point crushers are often installed for sometimes as low as 40% availability ie 10 hours a day or thereabouts, hwhere as the back end of the plant itself is probably dsigned for 90% availability.
The problem here is probably they got the ore hardness wrong.
The power required for a crusher runs around 1/10th that of a ball mill so there should not be an upgrade in transformers or gen sets.
The mobile crusher has proven that it can handle the situation in the interum.
Long term they need to design a different circuit ie jaw crusher as primary then a secondary cone type crusher and possibly a tertiary crusher. This is actually very easy to design and install , have a look at most large quarries supplying roading materials where they are in operation.