The DCO is a legal representation by the contributor to everyone who might ever use the code. It requires no second party on the other side to counter sign it or act as the receiving entity, so it exactly mirrors the inbound=outbound licensing model first coined by Richard Fontana.
All current Open Source CLAs are structured as agreements between the contributor and a second party. Most often, the second party is a Foundation or a Corporation, making them quite heavy weight in terms of setup, admin and overhead.
The main driver of community corrosion is the temptation to abuse a position of power (this temptation becomes irresistable over time because, as Baron Acton put it, “all power corrupts”). Since CLAs by their nature force a power imbalance between the contributor and the receiving entity, they act as focal points for this corrosion.
The way to avoid the community corrosion problem is to do everything minimally: use a DCO to take only the rights the downstream requires and to avoid all the heavyweight recipient, signing and tracking infrastructure.