That's a perfectly valid comparison. A year's worth of hours is still a year's worth of hours, regardless of what time span I spread it over.
We use this sort of formulation everywhere. If I say I work 40 hours a week, no one is going to assume that I start work at 9am on Monday, work non-stop until 1am Wednesday, and then take the rest of the week off. If I say that people spend approximately a third of their lives sleeping, no one thinks I mean that they sleep continuously from birth until they're 30 years old, and then spend the next 60 years awake.
We use this sort of formulation everywhere. If I say I work 40 hours a week, no one is going to assume that I start work at 9am on Monday, work non-stop until 1am Wednesday, and then take the rest of the week off. If I say that people spend approximately a third of their lives sleeping, no one thinks I mean that they sleep continuously from birth until they're 30 years old, and then spend the next 60 years awake.