I totally disagree.
We do not need more EU regulation as prices will jump sky high!
What is needed is more complaints to the companies themselve, on the web and for customers to get wise to the companies that do offer a better service.
Far too often, the problem lies with customers who want the cheapest car on offer for nothing! They then complain when something goes wrong. It doesn't work that way. Also having often seen the way many renters treat hire cars when on the road, its no surprise that clients get treated with short shrift.
When you've seen some irresponsible fool on holiday driving an expensive rental Opel cabriolet like a madman along a dirt track up and down a hillside or have been nearly run of the road by some drunk driving a small Group A car (Chevy Matiz) along a small beach side road at maximum warp and nearly rolling it, one develops some empathy for the attitudes of car hire companies.
Let Brussels get involved, watch hundreds of car rental firms and websites throughout Europe close up shop, with the resultant further increase in unemployment.
People should get wise. Search the web / tripadvisor before travelling and book with companies that have consistent good recommendations, EVEN though the price is a little higher!
Also as regards fleet/Group harmonisation, this would be impossible, given the permutation of number of models / engine size / vehicle types on sale though out Europe.
We need to get more self-responsible ourselves and get Brussels butting out of our lives not into it!
Finally, just aim for a car that suits your needs.
If one wants peace of mind, go with a reputable firm and ENJOY one's holiday. Then one does not have to worry!
By the way, the comments about also apply to holiday rental properties and hotels.
The number of people who come on holiday to the Algarve expecting and/or looking for problems has astounded me over the years. They go back as stressed as they came.
If one is coming on a budget holiday, because that fits a budget...accept it and enjoy it.If one can't, one may as well enjoy your break by relaxing at home at avoiding the strain.