I can see why Bill Walsh would pick those five positions first.
The QB, WR, and RB are obvious. Those are skill positions in which the offense will run through, but the QB at #1 is most important in a Walsh offense. If you have an elite QB, he can do a lot. A "perfect throw beats perfect coverage" every time. Also, when you throw in the fact that the Walsh offense was about quick horizontal passes, the offensive line isn't as important. And as someone said... we had Bobb McKittrick.
The pass-rusher and safety are obvious too from a defensive standpoint. I think most would rather have AWESOME pass-rushers and an average secondary over an awesome secondary and average pass-rushers. If you have a great pass-rusher, that pressures the QB into making bad throws. The Safety is that last line of defense and needs to be a good tackler.
It makes sense from Walsh's perspective. He ran a pass-first offense that would put points up on the board quickly. Teams would have to play catch-up and throw the ball late in the game, where pass-rushers and good safeties become even more important. If you look at how the Colts are built, it makes sense.
But there's no right and wrong way to build a team... Just depends on preferences. There's nothing wrong with what McCloughan has TRIED to build for our current team. I think he's really invested at the offensive line (Rachal, Baas, Staley, Snyder, Free agents like Marvel Smith, Jonas Jennings, and Larry Allen), but failed horribly this year. We've been building more towards what the Cowboys were in the 90s but haven't gotten the production out of our offensive line and Alex Smith. If these two spots produce, we're doing a lot better as a team.