As far as I could see, they were not that strict. As long as people were below 8kg, they were usually ok with it.
Not sure what you want to write them a complaint about, that they were sticking to their rules? I can tell you the kind of reply you will get: "We are very sorry that ... but ...".

I agree that 7kg can be restrictive, but when I know about it, I found it to be quite doable, incl. Laptop. I wouldn't necessarily use a 2.5kg carry on though.