Well I am kind of unique and have a pension that is paid by my employer, and I have a personal pension (sort of a 401K). Do keep in mind that pension fund in the Netherlands are really well guarded (loads of laws). An employer or intermediary could never withdraw anything (neither can you unless you are at pension age).
What happens in 20 years if the company hasn’t invested enough to pay your pension? A big downside of corporate pensions is when they fall short. For example British Airways has like a 3 billion deficit. I bet they wish they just got their money invested by a third party instead!
They have a payment obligation. Required by pension law. Employers are kept up to date by their pension funds (are required by law). Employers are always kept in the loop how their pension is doing and are offered the ability to add to it. There is even a limit into what you can add to it.
We also have a pension that is paid by the government. So in the end you get a sum: monthly income = government pension + company pension + personal pension (if you want one)