RG-400 heat resistance, moisture resistance, chemical resistance, corrosion resistance are all superior. About the only ways RG58 is better is cost and bend radius. RG58 may be fart lighter weight too.
You might think so, at ten times the cost, ten times the weight, and at these frequencies, marginally better performance. I've got some original RG-58 in a 1958 182A that is working just fine, thank you, and yes I ran a loss test on it a couple of years ago.