An angry Roger Cook has lashed as "east coast clowns" the people who authored an explosive report into GST distribution and branded it an "attack" on Western Australians.Western Australia was the only state or territory to benefit from 2018 changes to how the goods and services tax is carved up, according to a new Productivity Commission interim report into the reforms.The GST distribution is supposed to help each state and territory provide services and infrastructure to the same standard."However, as a result of the [2018] reforms, Western Australia received enough GST revenue to meet 113 per cent of its assessed fiscal needs in 2024-25 — compared with 98 per cent for all other states," the interim report said.Premier Roger Cook said any changes to the GST distribution would unfairly punish WA for its success "simply to prop up other lazy states".The WA premier argued that Western Australia and its mining industry prop up the rest of the country. (ABC News: Benjamin Gubana)He said the Productivity Commission's report was "an attack on every hard working Western Australian"."It's a sign that these east coast clowns simply do not understand Western Australia, they have no Western Australian representative, and no idea," Mr Cook said.The report said WA's mining boom drove up the state's ability to fund itself, meaning it received less GST, while the GST formula also meant WA was caught short when mining royalties fell after the global financial crisis."This produced a sentiment among many Western Australians that the state was 'losing' its revenue," the commission's interim report said.The interim report found WA had more money than was needed as part of the deal. (AAP: Joel Carrett )The commission said political pressure from the WA government at the time partially influenced the 2018 reforms.'Dodgy, deceitful, dumb'The Productivity Commission has proposed three potential options for change, stating the "first-best response" would be a return to the pre-2018 system, while addressing issues caused by mining revenue "directly and transparently".Premier Roger Cook and WA Treasurer Rita Saffioti held a blistering media conference on Friday after the report was made public.