That argument annoys me so much. Each vegetable does cover all amino acids, they just don't have them in the exact relations that our body needs. But if a vegetable has only 50% of one amino acid compared to the distribution that our body needs, then you can abso-fucking-lutely just eat double of that vegetable. Or as you say mix-and-match.
A typical Western diet includes far more protein than the body needs for maintaining itself either way.
Oh man, a few years ago, we had a military dude as conductor in our wind band. And I was always one of his favorites, I'm guessing because I have broad shoulders and a deep voice – prime military recruit material.
...except that I'm vegan. So, one day he sits next to me during lunch and asks me why I'm vegan. I do the usual dance of avoiding the topic, but he does not want to let it go. So, I tell him that I think killing animals is wrong. He walked out of that conversation like a hurt gazelle.
Like, fuck me, dude, if you're gonna do the whole military tough guy spiel, but cannot take a kid disagreeing with you, then maybe you're not as tough after all.