I was charged overage for the entire 7 kg at $15 per kg.

$15 per kg is 😱 🤦 the ripoff of the century. I understand charging people for excess weight but not like that. There should be a balance between the fine and the ticket price. In many cases you end up paying more than your ticket for just a few kg excess. It's not fair.

They justify this cabin baggage allowance by suggesting that the flight attendants can not be subjected to lifting more than 7kg at a time - which may actually be some sort of union bullcrap but honestly, how often do you see the flight attendants lifting anyone's carry-on?

This is also bullshit, as you say, you never see them lifting bags. I believe it's because of the size of the storage space above the seats.I've never had my cabin baggage weighed.

Unfortunately ticket buying has become more difficult as options are not included, you have to select them and you may end up paying a whole lot for not paying attention to everything.

I saw a situation at Budapest airport, a group of Chinese tourists, the first one had 3 kg excess and got a pass from the airline worker. Then the second also had a few kg more and he demanded to not be charged as the previous one wasn't. And so it went till the last one. The clerk was a young guy, and at the end he said the Hungarian Tax office is going to kill him for permitting so many excess weight without fining them.