Not true!
The proposal is no land and property tax up to property value of £135k
From £135k to £250k, you pay 2% on the value of your house above £135k
From £250k to £500k, you pay 10% on the value of your house above £250k plus 2% of £115k.
So for your example for a £300k property, you'd pay (115k*0.02)+(50k*0.1) =£7300. Currently, you would pay 3% on £300k = £9000.
I can't be bothered to do the arithmetic, but I think you start to 'lose out' if your property is worth more than £345k(ish)
At least that's how I have interpreted the way the tax will be imposed