I pay about 2400 a year for all my medical needs. That’s less than 1% of my income. Not even close to 8% and well below 420 euros.
Did you just argue that your $2400/year is well below €420/year? At current exchange rates it’s about $447, or about 18% of what you currently pay.
As others have pointed out, single payer is an overall cost save. It’s not hard to imagine creating a tax that companies pay to cover this with the money they will save from not offering insurance to full time employees.