A more appropriate comparison is straight horizontal lines for a given strength. For example, at 200 MPa, follow the line across. This will indicate how dense the alloys are in that area, and consequently how much it will take to do the job, for a desired strength. A vertical line will show much the same thing - how much strength you can get for the same density.
Just because the alloy used for strands in concrete is useful does not mean it is very versatile. Odds are you won't find that same alloy in many other applications, just like you probably wouldn't find a 1095 spring steel being used much outside springs or maybe knives. Many alloys are developed for niche applications such as that. Alloys like 15-5, 4340, 304, 1018, etc. would be considered much more versatile. Even magnesium, which you claim has no long term use, is flying long-term on nearly every aircraft you see. It has corrosion protective treatments like Keronite or Dow 7, and has been alloyed to not burn.
I'll give another comparison between 15-5 PH steel and 7075-T6 aluminum. Let's say a 1 foot long rod is required to hold up 10,000 lb, and both will be loaded right at their respective yield strengths. For this example, using the data below, the aluminum can carry the same load at at 15% less weight, albeit with a much larger cross-section (2.4 times that of steel). That's pretty significant.
15-5 PH
Density: .280 lb/in3
Yield Strength: 165 ksi
7075-T6
Density: .102 lb/in3
Yield Strength: 69 ksi
I'm not sure why you insist on trivializing the difference in specific strength between the metals.