The European laws are not some random thing we made up because we are lazy. It is to ensure workers are well rested and ready for a new working year. Hence in long term it will also benefit employers.
Some personal anecdata: I notice an immediate difference when I come back after a long vacation. The first 2-3 months I work at top efficiency, get probably done twice as much as I would do any other month.
In the case of the UK, much of the working hours, weekends, time off for bank holidays etc were hard-won agreements and rights from the Industrial Revolution era to the 20th century. The UK led the charge with many of these things too
I wish more people understood this. We had basically slave labour, workhouses, horrific factories etc