From a physics standpoint, yes, you're doing the same amount of work, and expending the same amount of energy, but from a physiological standpoint, no, they're not equivalent. You're depleting your muscles of energy at different rates, and incurring lactic acid build-up at different rates, so your body's response is different between the two.

The former (less weight/more reps) is used for endurance/fitness training. The latter (particularly if you're screaming in agony by the end) is for strength and bulk.

I would recommend you stop following Tony around, and speak to a fitness consultant at the gym. Tell him/her what your goals are, and have them help you devise a workout plan to reach them.

That said, perhaps your kayaking technique could use some refinement...