I don't know if it's because the rig was old, but the webbing was incredibly stiff and hard to adjust.
The webbing is impregnated with resin, that makes it stiff. I bought mine used and the webbing was just as you described. It was too short for me, so I bought new webbing and it was just as stiff and hard to adjust.
I think the DSS backplates are the only ones that have the rubber grommets (for lack of a better word) in the slot holes that the webbing goes through. Others that I've looked at pictures of just have bare metal slot holes for the webbing. I think, on those, you use an additional piece of tubular webbing as a sleeve around the harness webbing, where it goes through the slot holes. I assume that's to protect the harness webbing from rubbing on the bare steel edge of the slot hole and eventually cutting through. The DSS BP's rubber grommets seems like it would prevent that without using the tubular webbing sleeve - but, at the same time, make it harder to pull the webbing through the slot holes to adjust.
On the plus side, once the fit is dialed in, you shouldn't have to mess with it any more. And the DSS BP's rubber grommets seem like a nicer way to go than other BPs that just have bare steel slot holes.