It is not just marketing they are different oils made to sell at a different price point versus the competition. If it were the same oil beng poured in different colored jugs, at different prices, that would be just marketing.
The GTX Magnatec synthetic oil product competes with Mobil Super Synthetic. It is an older Castrol formulation that lets them compete at a lower price point. They are neither companies’ best synthetics. But all the oil companies have price tiers. Shell does not have a Pennzoil branding that competes in this arena. They have Quaker State synthetic at twenty bucks a jug and under, another Shellp brand.
The Castrol Edge is equivalent to the Penzoil Platinum and Mobil 1 product line.
The Castrol Edge Extended Protection and Mobil 1 Extended Protection are meant for 15,000 mile oil changes. As for Penzoil Ultra Platinum well hard to say really what that is intended for except to sell at the top price point as the other two, since Shell is unwilling to claim extended oil change intervals for it. Shell’s only claim is that it is cleaner than standard Mobil 1. I suppose Shell cannot go too overboard with their Pennzoil brand claims because it competes with their other, Shell Rotella T6 heavy duty brand that they are now marketing for gasoline engines as well as diesel.