This is a comment about attitudes at the end of the 19th Century. Various versions were documented in the 1880's, but the general form is:
Animals sweat, gentlemen perspire and ladies just glow.
Did ladies sweat? Of course they did, but it would have been very impolite to draw attention to this.
Did men sweat? Of course they did, and it was OK to talk about it, but you had to use a more refined word: perspire.
In these enlightened times, both men and women are allowed to sweat, but it is usually considered impolite to point out to somebody that they are sweating.
As was pointed out on that other question you linked, this is a surprisingly tricky sentence!
Let's slowly build it up.
It will take someone else.
What is "it"? Stopping Voldemort again. Implied but never directly said. As for "take", we could say "need" instead, just to be slightly clearer.
[Stopping Voldemort again] will [need] someone else.
This isn't "someone else" as in "we need a different person", but as in "we need other people prepared to do what you did, Harry". When will they be needed? "Next time" (that is, the next time that Voldemort tries to return).
[Stopping Voldemort again] will [need] someone else who is prepared to [do the same as Harry] next time.
Now, Dumbledore is saying that this someone else doesn't have to do much. Hence, it will "merely" (or "only") take someone else. This may sound like it's demeaning Harry's efforts, but it's meant to be reassuring Harry: standing up to Voldemort is not very difficult or unlikely after all, and it doesn't take someone extra-special to do it.
[Stopping Voldemort again] will merely [need] someone else who is prepared to [do the same as Harry] next time.
What, exactly, did Harry do that Dumbledore says they need other people to do (or be prepared to do)? "Fight a losing battle"--or what seems like a losing battle. (Dumbledore omits the word "like", but I'll leave it in for this one example.)
[Stopping Voldemort again] will merely [need] someone else who is prepared to fight a losing battle next time.
[Stopping Voldemort again] will merely [need] someone else who is prepared to fight what seems [like] a losing battle next time.
And now we just replace the bracketed bits with the different wording Dumbledore uses, and we have the sentence (okay, part of a sentence) that you bolded.
It will merely take someone else who is prepared to fight what seems a losing battle next time.
Best Answer
A person is not an event. The default meaning of miss when applied to a person is to have longing for reuniting with, that is, to an emotional response.
The sense of miss you mention when describing a boat, is not the boat itself, but the window of time when it was possible to board the boat. When we say we missed the last boat home, we mean that we missed the occasion of the last boat home boarding; when we arrived at the boat launch, the boat was no longer there or admitting passengers so we missed the opportunity to take the boat. In other words, an event, a happening localized in time.
It is possible to use this latter sense of miss to refer in the same way to people as to your example boat. E.g.
But note that to invoke this secondary meaning, there has to be some event that is pretty clearly alluded to. The deliberate absence of such allusion is actually a means by which wordplay is conducted on this pair of meaning, e.g.:
One way to disambiguate the terms is to use the idiom miss out on and which must always be followed by the opportunity in question:
Are you perhaps trying to tell someone not to miss out on some opportunity to do something with you? In which case you might say something like,
That would be well constructed English that will be understood in the way intended, though whether it is effective rhetorically among English speakers is a separate question.