I've found that the WHO's recommendations seem geared toward developing countries with poor sanitation, nutrition, and education. If that doesn't apply to you, they can be rather draconian.
Every time I hear some recommendation about solids, I hear about another new study that debunks the old one. Exclusive breastfeeding for 6 months used to be the recommendation, but a recent study from the British Medical Journal called that into question. I deeply question whether an infant needs only breastmilk for a year; a baby died recently in France because she was exclusively breastfed for 11 months and the mother had vitamin deficiencies possibly due to veganism. While it's true this could be an outlier case, even mothers who follow non-vegan diets are often encouraged to supplement their breastfed babies with Vitamin D.
Further, while a baby may not strictly need solids at any given point (4 months, 6 months, etc.) at some point, I believe from my own experience that it is helpful to introduce a baby to many different things to stimulate the senses. We expose babies to color and motion early, to many kinds of sounds, music and voices, many people, many textures, and I don't think taste and smell should be considered any differently. When exactly to do this depends on the child, but as an example, my baby was introduced to green beans at approx. 7 months and now screams like a banshee if she doesn't get them for lunch. I'm happy to have helped her develop a positive taste for them.
I feel that blanket policies about infant feeding can cause poor outcomes because there is such variation between infants and families that it seems useless to give anything other than general guidelines and then refer parents to their physician and their instincts for the rest. For example, policies like "breast is best" completely ignore all the times in which breast is NOT best--premature infants unable to breastfeed, infants with lots of food allergies making an elimination diet nutritionally unsound for the mother, mothers with insufficient glandular tissue, mothers with PCOS in which their bodies don't make enough milk, mothers with auto-immune disease requiring more energy than they actually have to breastfeed, mothers who have had breast surgery for cancer/reduction/reconstruction/etc.
Blanket policies don't take into account your baby and your situation, and taken to the wrong level promote lazy health care. A doctor who is pressed for time may just regurgitate the "recommendations" about solid foods without really taking the time to ask you about a family history of food allergies. In my case, my baby's pediatrician did a very good job addressing all my concerns about my and my husband's strong family histories of allergies, and we came up with some timetables for certain foods that differ from any of the recommendations I've read elsewhere. She was also very responsive when my baby showed signs of dairy allergy at 1 yr and was able to give us advice on whole milk alternatives--we didn't have to waste time going through the family histories then.
Even if there were official guidelines, I'd be very careful to take them as mere guidelines, not the hard and fast rule that "breast is best" has become despite ample evidence that one-size-fits-all medicine doesn't actually work for all.