£7000 savings/month for a captain with a few years in sounds perfectly reasonable to me. I'm thinking that assumes wife/kids, which obviously change the cost structure a bit. I was a single captain at the time and could fairly easily save about 12,000 USD/month on average without a monk's lifestyle. But if you wanted the boat and Ferrari well, yeah, the savings would be harder to accumulate. Then there were a few really uh, unique folks who chose to live in basically a cardboard box in the desert and live like paupers to save even more.
I just chose to live somewhere in the middle between the rockstars and the "vows of poverty" crowd. (The former outnumbered the latter by about 100 to 1, btw.)