Actually, I found the opposite, but my maximum age was 2 or 3 growing seasons. My wildlife trees got no after care once planted in the field and younger root-pruned trees do not have a large enough root system to get sufficient water during our summer period. My trees were all started from nuts or seeds indoors under lights in the winter. The trees that did best for me were planted after the roots filled 3 gall root pruning containers. By then the root systems were deep enough to get plenty of water during the summer. My fasted growing trees were transplanted twice (18s to 1 gal RB2, to 3 gal RB2) and had filled the 3 gals after a single growing season. Average trees, I overwintered and kept on my deck for a second growing season in 3 gals before planting.
Root pruning is not for every climate. It is a trade-off between faster growth and a denser root system for the grower providing water and transplanting to larger and larger containers until the root system is large enough so that it ha enough reach to access water during dry periods. I would not use root pruning in an arid climate. There I want a tap root to ensure access to water and I'll sacrifice slower growth for ensured survival during drought. In my area, root pruning is a great boost and produces great trees faster. Because the root system is so dense and has so many terminal roots, it is very efficient at delivering water and nutrients.
The point of my past was this . For bare root trees, we get the sleep, creep, and leap effect. For smooth container trees, you get circling and j-hooking roots that eventually limit the tree as they constrict themselves unless you manually prune them at planting time. If you do that, they are just like a bare root tree with the root system disturbed. With my root maker trees, the container unwraps and I slide the entire root system, medium and all, into the hole just large enough in diameter to fit. It is completely undisturbed and begins growing immediately. The lateral roots quickly penetrate my heavy clay soil that retains moisture well, so even though the medium dries out quickly, by the time our drier period hits in the summer, a 3 gal tree has plenty of access to water. Here, the top few inches dry out making planting directly from 18s a waste of time.
So, every technique needs to match the conditions. I've done both root pruning and direct seeding here. Root pruning works best for me, but that doesn't mean it will work best in all cases.
Thanks,
Jack