SAF was actually a massive attacking idealist for the vast majority of his time here. He didn't embrace pragmatism till his final years where he just became generally conservative from the pitch to the transfer market. The notion that SAF was a pragmatic manager is genuinely saddening when it comes from United fans because it means they genuinely don't remember a lot of his best years.
I don't think it's that straight forward to be honest. I think he was idealistic, but in a different way to modern managers. Modern managers tend to have ideals right down the tactical level of games. This might include things like how many players you have in the back line, whether you play single or double pivot, inside or outside wingers, always pressing high, etc. That wasn't what SAF was about.
For SAF it was more about the most basic principles of the game. His was more of a 'he who dares wins' kind of philosophy. He wanted his teams to continually pressure and attack the opposition, and would always be prepared to gamble. He very rarely would settle for a draw when a win was there for the taking.
However where he was more pragmatic was about how exactly he achieved that. He wasn't wedded to a certain formation, he wasn't worried about winning only via possession or counter attack, he'd do whatever was best. He wasn't worried about having certain types of wingers or certain types of strikers, he had all sorts over his career. If an outstanding player came along that didn't fit his system, he'd change the system, not the player.
In many respects, he was the highest level of idealist. He set winning above all else and would do whatever it took to achieve this. Compared to, say, his old opponent Wenger, who often gave the impression he'd rather lose than play football the 'wrong way'.