BIG oversimplification on the professor's part, to the point of making his statement not true. Yes the major nutrients plants get are N P K and those are in organic fertilizers as well as inorganic. BUT But that is ALL the synthetic fertilizers add. If you use compost to fertilize, the compost adds tons of trace minerals etc, plus lots of living biology from earthworms to microbes, protozoans, fungi, etc, plus tilth that adds structure to the soil and helps it to hold water.
reports a number of different studies of yields from organic and inorganic methods and includes this:
Soybean production systems were also highly productive, achieving 40 bushels/acre. In 1999 however, during one of the worst droughts on record, yields of organic soybeans were 30 bushels /acre, compared to only 16 bushels/acre from conventionally- grown [i.e. with chemical ferts etc] soybeans (Rodale Institute, 1999). "Our trials show that improving the quality of the soil through organic practices can mean the difference between a harvest or hardship in times of drought"
So, with plenty of water, the methods compared were about equal in bushels/ acre produced (though not necessarily in other qualities), but in drought times, the organic methods, with compost, did way better, through helping the soil hold moisture. Since in many areas, drought is becoming the "new normal," this will become increasingly important.
Also the N P K in chemical ferts, is not necessarily in forms that the plant can best use. Uptaking of nutrients by plants is a complex process, involving living micro systems. Read the book Teaming with Microbes, which we discussed here https://www.helpfulgardener.com/forum/viewforum.php?f=43
for lots more on some of these issues.
I could go on and on.... chemical fertilizing over time tends to decrease the fertility of the soil, since you are adding in NPK and taking out NPK and a whole bunch of other nutrients and since the chemicals (and tilling that goes along with them) tend to break down the structure of the soil and kill off the life in the soil. Chemical fertilizing has more negative environmental impacts not only in being a petroleum product, but for e.g. " 60% more nitrate was leached into the groundwater over a 5 year period than in the organic systems (Drinkwater, 1998)" [from the above article].
That's important because nitrates in the groundwater get into the streams and lakes and lead to their death through eutrophication (look it up!
And so on and so on!!