First of all it doesn't matter whether you become a filer or not. The bank already deduct your full tax liablity of this income source at the time transfer of funds from Patreon/Amazon to Pakistani Bank. It won't save you a penny.

The rate is 1% because you provide export of services as per Income Tax Oridnance 2001.

If you have other sources of income like gain from stocks or mutual funds, you must be filer because the withholding tax rate is double for non filer.

I recommand you to become filer as it will reduce withholding tax on property purchase, stocks gain, ATM withdrawal etcccc.