Your buddy doesn't know what he's talking about.
Sinew reflexes by it's surface grip, not by pulling both ends of the bow together as if it's a string along the back from tip to tip.
Composites are sinewed well short of tip to tip and they hold a little bit of reflex.
The technique of sinewing around the tips onto the belly of the bow is just to keep the sinew from peeling up under stress. not
necessary if your sinewing technique is good.