EU Consumer Law is NOT a warranty, nor is it a replacement for warranty. It's a lemon law. When you have a problem with a product you have to bring it to the manufacturer's attention (in this case Apple) within a reasonable time. Most consumer law states the first 6 months ownership. The manufacturer has to perform a repair and document the repair. Now, you state 6 years but most consumer law is 2 years. During the "6" years if you have the same problem and it's been serviced and documented by Apple then Apple will repair it. It's the consumer's responsibility to prove the issue they have years later is the same issue and cause of the first issue otherwise consumer law cannot force Apple repair anything.
"An Apple certified technician tells me that my logic board is broken. "
"Is this then covered under faulty hardware warranty?"
Did you ask this of the technician? If this is an authorized Apple service repair tech then he/she would know.