The claim is usually that diamond is the hardest material, which for the most part it is.
Strength is usually defined by the application and usually focuses on tensile / compressive strength. This is also why rebar is used in concrete, concrete has excellent compressive strength, but poor tensile strength.
There's lots of metrics for strength, also resistance to fatigue is often an important metric.
Diamond has excellent hardness, and compressive strength (diamond anvils), it's very poor in most other metrics of strength and evaporates above 450 degrees, so it's not good for anything hot.
Strength is usually defined by the application and usually focuses on tensile / compressive strength. This is also why rebar is used in concrete, concrete has excellent compressive strength, but poor tensile strength.
There's lots of metrics for strength, also resistance to fatigue is often an important metric.
Diamond has excellent hardness, and compressive strength (diamond anvils), it's very poor in most other metrics of strength and evaporates above 450 degrees, so it's not good for anything hot.