Nope, "units of work" is features delivered, bugs fixed, new people trained and so on.
As the parent commenter said, if you can do it in 2-3 hours per day -- this is great and you are getting benefits of being exempt.
Of course sometimes people pay you like you are exempt, but expect you to be present for 40 hours anyway like you are hourly -- and in this case, being exempt is a scam as the article said. But while common, this is far from universal.
Wrong: in a salaried job units of work is hours.
Unless your contract says otherwise.
> As the parent commenter said, if you can do it in 2-3 hours per day
You never do it in 2-3 hours per day, consistently.
If you are that good, don't tell anybody because they will start thinking they are paying you too much.
That's the opposite of how it is supposed to work when you are on salary.
You are paid for units of work, which is hours worked.
The output is not what you produced, but what the working force globally produced.
Being salaried means being paid a flat rate (forfait) for being there: sometimes you produce more (you lose), sometimes less (you gain), but the pay stays the same.