The last 2 posts are pretty much right. Key backs these days need to be able to run and rebound to release players up the ground and swarm fwd with numbers. Then belt back as needed.
The game i fear has gone past the bog bodied, less mobile backs like Astbury. His speed is poor and endurance not great. Hopefully im wrong on his prospecymts because we need him or another big body to step up this year. Otherwise the backline will leak.