And doesn't the gospel also claim that there would be a second coming in generations - hmm - don't think that happened.
Luke 21 is fairly clear that there will be an undefined period of time before the second coming, that includes the destruction of Jerusalem. During it, the Jews would "fall by the sword, be taken prisoner into all nations, and Jerusalem would be trampled on by the Gentiles until the times of the Gentiles were fulfilled".
Matthew 10 conflates the sending out of the 12 on a temporary mission, with the more general sending out into Israel after Jesus' ascension during which they should expect persecution and betrayal; they would not have finished this mission before the Son of Man came.
Matthew goes further in 16:27-28 adding that "The Son of Man will come in his father's glory with his angels, and then he will reward each person according to what he has done". This seems to describe the final second coming and judgment of the world, but then Matthew adds that some of them would still be alive to see the Son of Man coming in his kingdom. This refers to Jesus' ascension into heaven. Mark 16:19 tells us that Jesus was taken up into heaven and sat down at the right hand of God. This was the fulfillment of Daniel 7:13 in which Daniel has a vision of the Son of Man going into heaven with the clouds, approaching the Ancient of Days and receiving the kingdom. "In the future you will see the Son of Man sitting at the right hand of the mighty one and coming with the clouds of heaven" (Mt 26:64) refers to the same event, it is not the second coming but the revelation of his ascension into heaven. From that time onward, Jesus began to judge the nations, starting with the Jews and sorting out the righteous from the unrighteous. This is referred to in Acts 2 as Jesus "sitting at my [God's] right hand while I make your enemies a footstool for your feet". (In fulfillment of Psalm 110).
By the way, being a footstool for Jesus' feet means being under his rule. It comes from the saying, "heaven is my throne, and the earth is my footstool", which implies people being under God's rule.
So it is clear that Jesus' judgment of the nations, beginning with AD 70, is in view when we read the phrase, "coming of the son of Man". But also in view is the final judgment, when the last of Jesus' enemies to be destroyed will be death:
1 Corinthians 15:25-26,
"For he must reign until he has put all his enemies under his feet. 26The last enemy to be destroyed is death."
Matthew 24-25 conflates the judgment on the nations, starting with the Jews - called the revealing of the kingdom of God (Luke's phrase) or coming of the Son of Man (into heaven to receive the kingdom and reigning until he has put all his enemies under his feet) - with the final judgment of each individual:
"When the Son of Man comes in his glory, and all the angels with him, he will sit on his glorious throne. 32All the nations will be gathered before him, and he will separate the people one from another as a shepherd separates the sheep from the goats. 33He will put the sheep on his right and the goats on his left."
Thus we can see that there are two sides to the same "second coming" coin. One is a coming not in a physical sense, but Jesus' presence is manifest in some way, eg Revelation 2:5,
"Consider how far you have fallen! Repent and do the things you did at first. If you do not repent, I will come to you and remove your lampstand from its place."
The other side of the coin is Jesus' final coming back physically with the clouds, in the same way that he was taken into heaven (Acts 1:11).
We can see that although Matthew seems to confuse these two (like how he mixes two separate things in Chapter 10 - see above), there are clear references elsewhere to an undefined period during which Jesus rules in heaven before he finally hands the kingdom back to the Father (1 Cor 15) and everyone will go either to eternal punishment or eternal life (Mt 25:46).