That was the consensus during the season too and it was wrong. Duncan was a big and he was practically clowned by Bogut in the paint. Side show Boban was a big but wasn't caliber enough to even see the court. Oh, you must have meant QUALITY bigs. You don't make two straight NBA finals appearances by being a one trick pony. If it was that easy to add a little size to a team's roster in order to thwart the Warrior's success in a playoff series, everybody would do it. So you score a few more baskets in the paint and lose by 15 instead of 25. The Grizz (2015) and Thunder (2016) both had size yet, they still lost.
The Spurs priority in the offseason was to add depth. They need a full roster or close to it so Pop can rest it.

They went after size in the offseason, not so they could exploit the Warriors weaknesses, but so that they could have more versatility against the league's elite, like the Thunder and Clippers who had a size advantage. The Spurs are all about shoring up their own weaknesses rather than trying to play wrecking ball with one of their rivals. The Spurs organization is far less obsessed with the Warriors than the fans and media alike.