Would that be a foolish wager just because that's the nature of the beast? Meaning that no deck stain/sealants last longer than a couple of years?
Yup. There are just too many factors effecting any stain product. I do think there is a big difference between having to complete strip a product every couple of years and touching it up.
I think any deck owner should plan and budget time and money to attention of the finish every two to three years. If you get lucky and the materials used last longer you are ahead. If not, you at least planned for it.
If you are only getting a season of use out of products, I would start to think about whether they are the wrong products.
Solid stains on decks, with a good quality product, last 2-3 years. Semi-Transparent finishes, maybe a bit longer than that. It depends on the climate and environment where you live. There is maintenance required to keep the finish looking good.