I believe it's an easy solution as long as everyone agrees to fix it.

Therein lies the rub. Getting everyone to agree to fix it. Everyone has there own agenda, governments have their own agenda.

The end result is that everyone is paying GST on everything, but companies can claim a lot of GST back

The fact that companies can claim a lot of GST back, it's basically a pass thru tax and the end user is the one that pays for it. Governments need to stop increasing GST/VAT and I don't know raise revenue another way whereby citizens don't bear the full brunt of it.