For unselected seedlings and daylilies that just aren't drop dead gorgeous and/or great performers, yes, I can see 2 years being long enough.
But (for example) I've had 'Osterized' and 'One Fine Day' for many years, and I don't anticipate booting them *this* year. I always look forward to the first one, and the second gives me reliable early bloom and fall rebloom, and the flowers open well during those time periods. Maybe they aren't all drop-dead ruffly gorgeous, but they serve me and the garden well (and have not yet gotten more than a speck or two of rust) - whereas it is a crapshoot with respect to anything new coming in (blooms can't handle our cool nights, the plants get rust, and so on).
So while I, too, like to see new plants (I want to get some more Davisson daylilies this year), there will always be some "oldies but goodies" in the garden.
