Aluminum and magnesium are lighter than titanium at the same strength.
The idea is you can use less titanium in the application you would use aluminum, but this has limits. If your ladder was .200” wall thickness, you might in theory get away with a .070” titanium for the same weight, but you start running into mechanical stresses or assembly issues or manufacturing.
Titanium is useful when you need internal volume - most recently as an example by Apple. Aluminum was fine, but had thick walls. Steel allowed thinner was but was heavier. Titanium allowed for thin walls and more internal volume, but at a higher cost.
Basically, if you don’t have a size limit, aluminum is great! But most things have size limits, and titanium allows you to trade size for cost.
The iPhone 15 pro is mostly aluminum. There is about a 1mm thick band of titanium around an aluminum frame.
https://www.apple.com/newsroom/2023/09/apple-unveils-iphone-... https://www.youtube.com/watch?v=S_W73ouKtjU&t=605s
And that makes perfect sense.
Thick walls on the iPhone are what are going to prevent X Y area which I suspect they need more than thickness.
Seems like marketing to me. They got rid of the stainless steel frame from previous models, switched back to aluminum, then added a pointless band of titanium so they could say Titanium in their marketing.