The Mavs have not been treated as the defending champs all season in the games I've watched. I really do think the shortened season affected their chances of repeating. I also blame the shortened season with condensed games for many of the players injuries, even if it's not directly related.
The Spurs have been playing great basketball. Every year I rule them out as a contender, but they Popovich and management has done an amazing job. As a franchise, I believe they have won 50 or more games 12 consecutive seasons now, even during the shortened season this year. That consistency is amazing.
I do hope the East gets more interesting though.