Amino acids are the building blocks of life and the birds can’t get that only from flowers although the flowers contain small amount of proteins and salts. Calcium is also mandatory for birds to strong their bones and making the egg shells. That’s why the birds get all these nutrients from other insects. Normally Hummingbirds steal the insects from the spider webs and maintain their calcium level. They also eat the gnats and aphids.
Yes the birds need all extra supplements for their other needs but we are stick to their simple nectar food with 1:4 ratio because their digestive system is not to string. So be safe and feed the birds with simple nectar. Moreover the birds can get the calcium and other nutrients from insects and invertebrates throughout the year.