I've worn SOOOO many harnesses out - sometimes pretty fast.
Especially earlier when it was about riding TT's really powered and jumping MAX, and using seat for this very purpose - I could destroy a harness in less than a year sometimes
Waist harnesses last somewhat longer, yes, as you can not hold the same amount of power down, and it also slides more, so you dont always get the same hard yank when jumping - so besides being "simpler" thus less prone to wear, it is also less "spike" loaded in jumps.
But they will still wear, both the fabric because of sun and salt - and especially the belts will "tear" more and more at the ends of the spreader bar.
Now, mostly riding waves with less power and waist - my harnesses last about 1-2 years (have had lots of different brands, and always a spare with me so I wont loose a session).
77kg and out +150 sessions a year.
If you are heavier - the harness will wear A LOT faster.
Time on the water (session and number of hours) is really important.
If out less than 100 times per year, it will hold much longer of course - and if only out a couple of hours each time - it will also hold up better
There are differences in different models and brands - but I've found the belt to be the weak link in all of them, and in the long run not that different how fast this wears
With seat harnesses, the leg strap stitching is the weak link, and sometimes also the plastic snap locks - besides the belt wear.