This is simply incorrect.
SG is the higest rated oil of ALL oils with 0.12% of zinc allowed. After this ALL grades of oil contain less in order not to affect the sensors for engine management systems.
Worse still is that any oil rating is the MAXIMUM that it WILL NOT reach. So an oil can have no zinc and fully comply with SG, SF SH SL and all the rest because it has LESS additives than the maximum allowed by the rating.
As an aside, an oil which has 50 in its weight is excempt the maximum figure for additive concentrations as these oils are designated for old engines without engine management systems. So a 20/50 oil MAY contain any amount either less or more than the 0.12% allowed by the SG specification. BMW oil (20/50 dino) used to contain over three times the 0.12% Harley Vtwin oil (20/50 dino) still contains more than twice the SG rating.

A good strategy for choosing a suitable oil is
1. Select the right weight for your engine at the expected operating temperatures. Too thin will cause low pressure when running low revs and hot. Too thick will cause oil starvation and bearing burnouts. Both conditions particularly apply to white metal big ends.
2. get the highest rated oil with which your engines electronics can operate safely (too high additives can destroy sensors) If you engine management system is entirely your right wrist ignore this as you can use as high a rating as you wish.
3. IF your engine and gearbox share the same oil, synthetic would be a good choice as gearboxes really chew up engine oil quickly.
4. If your engine and gearbox run separate oils use the grades recommend and you are unlikely to have any problems. Same applies to Primary transmission.
NOTE, IF your bike has separate oil for engine, gearbox and primary ( if it has one) then this type of construction is much kinder to oil and give you a much wider choice and longer oil life which is why dino oil is often used.