I do not see it as a headache. I am fine with doing whatever needs to be done, but the description of what needs to be done changes every time I speak to a new assistance in the Tax office. Today one of them told me that a correction could not be filed, instead I had to wait for the tax form and send it back with my corrected salary certificate explaining why I was not supposed to fill it.
In terms of how much of a hustle filling in the form is - happy to do it, given it leads to a refund.
They usually assume some standard deductions, e.g. travel pass. I don't know details probably written somewhere. For example donations are deductible and not taken as standard dedictible and up to 20% of your income worth donations can be deducted from your tax.
There are also things that can make you pay more money. For example if you own an apartment that may increase your taxable.
But earning 125 vs 120 on its own is not much of difference. You will pay extra tax only on the 5k at whatever the applicable marginal tax rate is.
Also note that once you fill in those forms you have to do it forever as long as you pay tax in Switzerland.