Luxury/sport vehicles tend to be new enough to be at least euro 6, despite having very large engines and often fewer seats, thus much higher volume of emissions per passenger compared to a small older car. Also, the fixed fee hardly matters for rich people, so even old luxury/sports cars are de facto exempt.
Taxis are exempt, despite plenty being diesels older than even euro 4.
Plenty of delivery vans with significant emissions are de facto exempt because the fee is negligible when compared to other expenses.
If the fee was at least a percentage of income/revenue or a percentage of the value of the vehicle, it would be a bit less bad. If it also scaled measured emissions by passenger instead of using the flawed emission standards, then it might even become useful. If it also included free vehicle replacements funded with revenue from the taxes on the excessive cars, then it might even be good.