Do you consider yourself fit because you lift? Maybe my definition of fit is different than a lot of people. IMO, fit people have a high baseline in three categories- strength, endurance, and flexibility. If you’re lacking in any of those areas, you’re not fit. It’s an incomplete package if a person only excels in one area and not all three. The body is a system and it’s not the most efficient system without all three components. You don’t do cardio so you get winded going up one flight of stairs. That makes sense since this isn’t an area you work on. It’s a little troubling that your cardio baseline is so low. It’s akin to a smoker’s cardio baseline. You may want to improve that.

I walk up 6 flights of stairs without getting winded and I rarely exercise. I am most certainly not fit. When I did lift, I still had trouble opening certain windows at work. At that time, I carried a 50lb box up 6 flights of stairs with no problems. But that same week, I couldn’t open the window in the work bathroom. That hurt my pride.