When you fit a bike perfectly there is
no need for headset spacers.
Sure, I suppose. With minor adjustments in the saddle and bars, perhaps, everything else is at the "right" spot.
But over more than four decades of cycling I have yet to find any bike fit "perfectly" for me. There are always minor (sometimes major) misses in what the designer imagined for the geometry and what my specific body and riding style dictate. Usually, overcome with simple saddle/stem/bar changes, though occasionally impossible to the point of that specific frame being inappropriate for me.
I suppose that the old "ten speed" from the '70s fit sufficiently well, but then I was young and strong and it pretty much didn't matter that much to me that a fit wasn't "perfect." Its top tube was probably an inch and a half too long for me, more or less, and (for preference) I probably could have used drop bars with far less drop in them. But it was close enough to work well.
What seems to work best for me these days: reach of about ~350mm, stack of about ~550-570mm, bars with some rise/sweep, for a more-upright riding position and more-pedestrian pace than in past years. (Getting older has its pros/cons.) Not a lot of standard, off-the-shelf products meet those basic measurements. I've found on some frames putting a good inch or two of spacers beneath the stem is sufficient. On my current bike, I'm at the limit of the steerer tube already, so any significant adjustment upward (beyond the adjustable stem) would entail a longer steerer on a new fork, though keeping the same geometry of the current frame. Usually, I've ended up with a different stem, bar and saddle arrangement, and that's been sufficient. Works well for my own limb/torso length and riding style.