Similarly, it's a "complete" protein, whereas most vegetables and legumes are missing necessary amino acids.
The downside of beef isn't the "density" of nutrients: the downside is high saturated fat. Chicken breast, though, is similarly high in protein without the saturated fat downside.
There are other downsides to beef .. such as the batshit crazy use of ecosystems and resources required to produce it at industrial scale.
Got a (beef) cow roaming in your yard, somehow getting by on whatever grows out of the ground? Enjoy your steak! Generating 6x the calories via a water-intensive cover crop to feed the cow so you can eat it later? Just say no.