You'll have to explain further your interpretation because that isn't how I read the legal interpretation.
Matter of fact - it says that if you were serving as a -121 PIC on the date before the rule went into effect (and if you didn't yet have 1,000 hrs of -121 time total) then you are grandfathered in - pretty smart move.

I think what may be confusing you in the paper is the scenario where the person HAD served as a -121 PIC, was not employed as a -121 PIC (or in any -121 operation) at the time of the rule implementation, and now the prior flight time will not count towards the 1,000 hrs required for upgrade. In that case - yes - it seems that it is a start over for that person that left the airline business.

More concerning though (to me of course) is to find out that my P135 PIC time will not count towards my 1,000 -121 time for when I bail to the airlines!
Or not.