I agree that play is more important than PC building. But I haven't had the experience that Schwalb and others describe, of having PC building be more important than actual player decisions at the table in determining what happens.
The following list of encounters is still, I think, the busiest "day" the PCs ever had in my 4e campaign (ie activities undertaken without an extended rest):
*Comp 2 L14 skill challenge (as a result of which each PC lost one encounter power until their next extended rest);
*L17 combat;
*L15 combat;
*L7 combat;
*L13 combat;
*L15 combat;
*Comp 1 L14 skill challenge;
*L16 combat;
*L14 combat;
*L13 combat;
*Comp 1 L15 skill challenge;
*L16 combat (the L15 solo was defeated by being pushed over a bridge down a waterfall);
*L15 combat (the solo returned later in the night, having survived the fall and climbed back up).
The PCs started this day at 14th level, and finished it at 15th.
And the action was all about playing the game, not just mechanically deriving mathematical consequences of PC-build choices.
Also, the idea that 1st ed AD&D was all about play and not PC building doesn't fit with my experience at all - one of the most important determinants of success in AD&D is caster spell load out, and what is that if not a PC build decision? (The fact that it's flavoured as an in-character choice doesn't mean it is actually part of engaging with ingame situations at the table!)