The DG is voluntary. You are not entitled to anything beyond that which you negotiate. If it's EUR300 + fare difference, that's what you get. If it's EUR300 and a cup of coffee, that's what you get.

The issue about who is entitled to keep the compensation is between the pax and his employer. Some would not allow an employee to accept any voluntary offer, some might insist on receiving the compensation and some might just let it go.

Snarky comments to low-level carrier employees demean the employee (involuntarily) and the pax (voluntarily). If you are offered something and don't want it, just decline. There may well be someone behind you who wants it and takes it.