Curtis wrote:

I have a floor joist that is sagging where the joist was drilled ...
Naturally this hole was made in pretty close to the exact center of the
joist

If the hole was centered in the depth of the joist the effective strength
has barely been reduced. The sagging most likely was due to the dead load
over time.

Spars in aircraft wings have lightening holes for nearly the total span.

If you read his second explanation you find out that the
hole is center in the narrow edge and reaches from the top
to the bottom of the joist. This would effectively change a
1-1/2" thick joist into a 1/2" thick joist assuming the hole
is 1' in diameter.