I can't believe you're saying one skater doesn't matter much after what Kovtun just delivered in the SP. Can you imagine if he'd skated like that at the Olympics, at the first competition of the team event, and placed last?

Not just the loss in points, but the psychological effect on his teammates. People like I/K, who were known to be quite inconsistent, and could very well have botched a lift or fallen on twizzles had they skated with Team Russia in a deficit.
Same goes for Mirai: what if she'd showed up at the Olympics with her Skate America SP from this year? Granted, they could've made Polina do the Team Event instead, but I can see why the USFSA was hesitant about going with someone really inconsistent (Mirai) or someone skating in their first international competition (Polina). So they put their faith in Ashley, and it paid off.
I would've given Boyang Worlds over Nan Song, but the examples you're using hardly work. Those people were selected for relative consistency and scoring potential, despite bombing one competition (Nationals). Nan Song, unfortunately, doesn't seem to have either scoring potential or consistency. A shame, since he didn't do all that badly jumps-wise in the SP... just needed a level doctor and a completed StSq.