I was listening to Suratal A'raaf yesterday and this is what I came across (and Quran uses this term through out):
قَالَ الْمَلَأُ الَّذِينَ اسْتَكْبَرُوا مِنْ قَوْمِهِ لِلَّذِينَ اسْتُضْعِفُوا لِمَنْ آمَنَ مِنْهُمْ أَتَعْلَمُونَ أَنَّ صَالِحًا مُرْسَلٌ مِنْ رَبِّهِ ۚ قَالُوا إِنَّا بِمَا أُرْسِلَ بِهِ مُؤْمِنُونَ
The chiefs of the arrogant from his people said to those weakened from those who believe, do you know Salih is sent (mursal) from his Lord, they said "what he is sent with we believe in".
It can derived from this, the meaning of "sent" is to be sent with "something", that the believers said "what he was sent with we believe in".
So the meaning of "arsal" with respect to humans takes on this special meaning, that God sent them with something to be believed in.
The words Musraleen, arsal, mursal, are all over Quran, and they have this meaning whenever applied to a human.
So God he sends humans with either:
A revelation in a form of divine book/scripture to be held on to the people like Torah and Quran.
A message or messages from God they must deliver to the people and convey the clear message in this regard.
Or both (most Prophets and Messengers were both).
To know it doesn't mean "sent" as in the person is sent without a message, is that Mariam and Sarah are chosen and brought to humanity as chosen ones, but they aren't "sent" who other verses show are only male.
It's important to not just look at ahadith as what they can mean linguistically but they compliment the Quran and Quran should be taken account to what words it emphasizes on.
As we know God ended Prophethood in Chapter 33, he made it clear Mohammad is the final Prophet, so this means the Mahdi is NOT a Prophet, but he is coming with a message or messages that will revive the Quran and Sunnah.