Dear I'm not aware of level of understanding about Mantle that you've. There are two considerations about Mantle which makes it really a must have:
1. Mantle provides the ability to have 80,000 to 90,000 Draw Calls per Frame as compared to DirectX or OpenGL and current configurations reaching 3,000 to 5,000 Draw Calls per Frame. This would enable the GPUs to improve the performance of Draw Calls they are making because telling cpu to draw 90,000 objects on screen in one go would otherwise be dependent on GPU itself.
2. Mantle is designed for modern hardware. This is a basic limitation of DirectX because when DirectX was released there was no dual core or multi-threading hardware. Mantle's API is of lower overhead. It means the Mantle uses or speaks the same language which the GPU's native architecture uses so there would be less dependency on the CPU to do translation hence eliminating hardware downtime.
3. In coming times, AMD is hoping that Mantle would become Industry Standard like DirectX and all developers would be using it to deliver Mantle enabled games likewise, gaming enthusiasts realizing the performance gains would be demanding it as well.
4. It is time bound what would happen! But from hardware dependency point of view Mantle is set to change that. It is for sure.
5. For nVIDIA users, although AMD has announced it to be an open API, much would depend upon nVIDIA's reply and stance over it.
If you've more info and opinion pl share.