It's not. Precise enough, that is.
There's a point in the ILS landing process called "Minimums". At that point the pilots must see the runway or throttle up and go-around. Assuming they have seen the runway, they must be prepared to stick-fly it onto the centerline, and then keep it on the centerline during braking, against crosswinds (still pushing on the tail), asymmetry in braking or reverse thrust, etc.
The precision of this varies by different classifications of wayside and on-airplane equipment, so both minimums and the "when you take over and stick fly" points also vary (separately). You can't decree that every landing airplane has the latest & greatest.
In fair weather, SFO ops (when my cubicle was directly under the flight path) involved bringing in airplanes near abreast, virtually wingtip to wingtip. That's not the computer either. That is the slightly trailing plane stick-flying it, using the Mark 1 eyeball for separation. And that depends on both fair weather and a high cloud ceiling, so they can visually line up (with each other) early in the approach.
The abreast (not staggered) approach was required for capacity reasons, not for landing but for takeoff: these two aircraft needed to land simultaneously and clear the runway intersections simultaneously. There were two departing aircraft lined up on the two cross runways to start their takeoff roll the moment this pair swished by.
I've even seen a triple: a Japan Air Lines 747 and two F-16s. Guess which day it was.