> most vegetables and legumes are missing necessary amino acids

In practice, there's no evidence of amino acid deficiency in vegans/vegetarians except ones that restrict even further (potato diet, fruitarians, etc) https://pmc.ncbi.nlm.nih.gov/articles/PMC6893534/

Besides the ever-popular soybean being a complete protein, if you have normal variety in your diet, it's just not something you have to worry about.

The fat is an excellent source of energy though and it's very hard to get fat by eating fat because it's essentially hormonally inert. I.e. eating fat doesn't precipitate insulin which is the hormone that enables body fat accumulation.

So the problem with steak isn't the steak itself it's the "steak dinner" where the meat comes with sides such as french fries and drinks such as beer.

> Beef has ~3x more protein per gram than legumes

   - Chicken: 27/100g
   - Beef: 31g/100g
   - Hemp: 32g/100g
   - Pumpkin: 33g/100g
   - Soy: 36g/100g
   - Seitan: 75g/100g

Eating only one type of food is not good for your health, whether it is a plant or animal product.

> The downside of beef isn't the "density" of nutrients: the downside is high saturated fat.

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.

Worth noting that like amino acids there are essential fatty acids as well, and most people have poor nutrition there... red meat isn't "only" saturated fat, but a fairly balanced fatty acid profile. You can have too much, but in moderate cuts it isn't too bad.

I usually suggest around 0.5g fat to 1g protein as a minimal, higher if keto/carnivore.