Possible explanation of the "7 year" comment getting tainted - some airlines had, and might still have, a drop dead at 7 years in one seat. They've seen too many people 'hide' in a seat. They prefer to see that you exposed yourself to a training environment and switched seats, or equipment, in the last 7 years.

Your current path you estimated getting to 1000 hrs Part 121 TPIC in 7 years. Going to a regional might get you that in 4-5 years at the earliest. That's when you'll be the most competitive. Getting 2000 hrs more 747 SIC time isn't better than 1500 hrs regional SIC and 1500 hrs regional PIC.

As an inexperienced guy you need to get more ups and downs. With a bunch of long legs you might be getting 25 landings a year. You'll get 25 landings a month at the regionals.

Good luck.