Here's my thought on "holding" a selfbow or all-wood bow at full draw....
A wood bow is as near to it's breaking point as it can be at full draw. Maximum stress on the limbs - whether you believe it or not, bows don't last forever, and wood bows probably the least of any. This is simply due to the materials, assuming workmanship is top-notch. This doesn't mean a wood bow won't last many years, but it won't last as long as more modern trad bows with superior materials. That's why certain species of wood are better to build bows with.
Think about bending a steel rod over and over again...at some point the "weak spot" will be overcome and the steel will break. Same with a bow. Wood bows only possess a limited number of "shots" or draws in their lifespan. To draw a bow to it's full potential (full draw) is making the wood undergo it's maximum stress. Holding that bow at full draw, it seems to me, bleeds the life out of the wood. The less you hold, IMO, the longer that bow will last. That doesn't mean you should go and radically change your style of shooting, but there is a lot of misinformation about these bows that gets thrown around that isn't entirely true.
The 3-under tillering thing is no problem. I've built and shot and hunted continuously with wood bows now for 30 years, and I love the things....but they are not as durable, as fast, as easy to "master", as more modern traditional bows. Some will say they are...and "some" come close to being "there", but in general they are more challenging period. But....and many never get this point...that is the thing that makes them and your experiences with them more special, and more rewarding.