Fact One: Not all pollen is equal.
Fact Two: No pollen and the colony dies.
Fact Three: There is no such thing as a 'complete' pollen substitute.
Pollen is essentially the male sperm cell of flowering plants. The pollen grains themselves come in different shapes and sizes.
The test to classify pollen for its value to honeybees is to measure the Crude Protein content. The Crude Protein (CP) content of pollen varies dramatically. South Australian wattles have low CP content while canola CP content is high. The CP content has to be 25% or better to be considered good to high value for bees. Salvation Jane was once the most valuable plant for beekeepers with a CP content of 37.4%. Now Salvation Jane is a controlled weed.
If your bees are collecting pollen from a variety of sources, you will have multi-coloured pollen stored in the wax comb, and your colony is doing well. When the volume of pollen is limited, then there is a nutritional deficiency and a declining hive. This need to be addressed by the beekeeper. Either by moving the colony to a better location or providing supplemental feeding of a pollen substitute.