What is a synthetic?
If I take a car and change the exhaust to a sports exhaust, it is now a "modified car". Its performance is enhanced through modification!
The same with oil chemistry. You take a mineral oil molecule, take part of it off and add a different short molecule to give enhanced characteristics, you now have a "synthetic oil". It is that simple.
The problems occur in the processing. All the old molecular segments need to be cleaned out. -various procedures are involved at differing costs. At the end of the day, a well refined mineral will do you more good than a cheaply refined synthetic, regardless of the grouping or the classification.
Most oil on the market is sourced from crude oil, as is the plastic chair you are sitting on, the varnish on your furniture, etc. The only exceptions are castor oils (Last used in factory racing in 1975), some esters (most esters are from crude oil stock -go read your chemical engineering handbook)and polyolesters (although these can be made from crude oil stock, the are in reality always plant based as there is higher oxygen double bonding which gives them much greater strength in temperature , shear strength and lower friction coefficients -all modern jet turbine engines use polyolester. Ask you local Boeing 747 mechanic!)
Another problem: Modifying molecules is always a compromise. eg. PAO. Very slippery. Very little film strength, so will have very large amounts of friction modifiers to cope when metal to metal contact occurs. That is why you can run an engine with flat top tappets on a basic mineral oil(much higher film strength than PAO, but if you run this same engine on the "superior" PAO, it will destroy itself.
It is all about horses for courses. Know your requirements. Get an oil to match those requirements.
Food for thought: Why does the modern aircraft industry only use the most expensive oil commercially available, being, polyolester? Because in the long run it is the most economical way to operate.