I mean, I obviously agree that the complication in the US tax system is crazy, and also think that every country should do what the UK does in allowing PAYE income taxation (Pay As You Earn - most people in standard jobs have their company take the correct amount of tax from each salary payment and pass it direct to the government, the employee then doesn't even have to file taxes at the end of the year unless they have special circumstances).

But in this specific case of "minor error [...] leads to significant money losing tax implications" - it is really an error that would be possible in absolutely any "fill in your tax info situation", since the mistake they made was writing the wrong number into a "taxable income" field. That mistake can still be made even in a country whose tax system is as simple as "everyone pays X% of their income as tax, and fills in a one-field form where the only question is "what was your income for the year?". (But yeah, a simpler system would mean less opportunity for making simple mistakes, and easier to check if any have been made, for sure.)

The IRS has actually caught some that I've made, the only time they've ever complained to me has been to send me a larger check. First they send you a scary looking notice that they detected a discrepancy, and you have to agree, but each time it was an error that when fixed improved my refund.