I think if you fished the same line 3-4 times a week, you might only get a season or two out of one.
I fish 5wts almost exclusively, but use cane rods which are probably easier on lines. I’m more likely to do something idiotic (like step on a line with studded boots or let a fish wrap me around a rock) to ruin a line before it wears out, but I hedge my bets — I use DT lines, so I can just swap ends and keep going.
With that in mind, I’ve got a pair of Cortland 444 (peach lines) that are 4 years old, though one recently cracked and passed onto the next plane of existence, which fits with my intial estimate.
I expect my WF7 Air Cell Supreme to last a decade given it’s only used during the stonefly hatch and for the Rogue’s summer steelhead.
TC