Although i agree with your point about eddy currents.
But the amount of eddy currents depends on the thickness of the "layers"
Also they can add upto 3% of silicon which increases the resistivity upto 4 times.
Have a look at the following schema (sorry its djvu) http://www.eserviceinfo.com/downloadsm/828/Philips_K-9.html
In the powersupply You will find T182 which is a laminated core (2 C-cores) and it runs at 18 or 15 Khz (sorry its decades ago i been fixing those tv's i am not sure on the frequency)
This powersupply was very reliable and those tv's sometimes made over 25 service years .
During my own experiments with laminated iron cores losses were acceptable upto 30 Khz.
(do keep in mind this transformer (and core) was specially wound for us it wasn't a standard of the shelf 50Hz core)
Ofcourse You shouldn't push the limits because the losses would be horrible and ferrite would be much more efficient.