I'm not clear what you're arguing here.

When I evaluate an hourly rate, I multiply by 2100 and ask myself if this is a reasonable salary & benefits total package.

So if my rate is $125 an hour, that comes to $263k, which is a base salary of around $200k plus healthcare, self-employment taxes and sick/vacation time, etc. Now my healthcare costs might be lower than others and I don't factor in retirement because I work primarily for startups, but again this is why each contractor calculates differently.

I wouldn't multiply it by more hours if it was insufficient, I would just raise my rate.