The other scriptures you are referring to do not describe the second coming as they contradict that clear description by the angel.
They describe God’s judgement on Israel for crucifying his son using the often used metaphor of “coming in clouds” and “sun and moon” no longer shining and “stars falling.” Those passages exactly are used in the OT to describe the end of an evil people group.
The context for Matthew 24, Luke 21, and Mark 13 are as so:
Matthew 24: 3 As he sat on the Mount of Olives, the disciples came to him privately, saying, “Tell us, when will these things be, and what will be the sign of your coming and of the end of the age?” (ESV)
Luke 21: 5 And while some were speaking of the temple, how it was adorned with noble stones and offerings, he said, 6 “As for these things that you see, the days will come when there will not be left here one stone upon another that will not be thrown down.” 7 And they asked him, “Teacher, when will these things be, and what will be the sign when these things are about to take place?” (ESV)
Mark 13: 3 And as he sat on the Mount of Olives opposite the temple, Peter and James and John and Andrew asked him privately, 4 “Tell us, when will these things be, and what will be the sign when all these things are about to be accomplished?” 5 And Jesus began to say to them, “See that no one leads you astray. (ESV)
Overall, the whole context comes from the previous chapters where Jesus, as usual, is battling with the religious leaders and exposing how they corrupted the law, etc. Matthew ends this confrontation with a lament over Jerusalem. Yet, when comparing all three, you can't ignore Matthew 24:3's "
the sign of your coming and of the end of the age" and while Luke 21 and Mark 13 don't put that line in their handling of the Mount of Olives lecture, it is the context when you get down to Luke 21:25-28 and Mark 13:24-27. You have to remember, despite our translations creating sectionals, chapters, verses, paragraphs, sentence breaks, etc. This isn't in the original text and this is recording one whole speech that's attached to the question the disciples ask him at the beginning and, yes, while the, at that time upcoming destruction of Jerusalem is included in the speech, it goes further beyond that event in history to events in the future.
The problem with limiting the Mount of Olives lecture only to the events of 70AD is that Jesus includes in the sequence of events a collection of things that did not happen in 70AD, a collection of things that have happened over the ages, but the key is that he says that the tribulation he's talking about will be such a tribulation for believers that has not been seen since the creation of the universe until now
(for the disciples then) and will never be seen again. If everything that happened in 70AD and with Nero, etc. is what Jesus was talking about with the Mount of Olives, and none of that was supposed to be ever seen again, why have we seen consistent persecution of believers in some way and similar ways long after the Romans did what they did to the Jews? And Jews have been exiled from countries since then all the way up to the middle ages for various, sometimes very silly reasons.
I don't limit the celestial signs to just metaphors. Seems to be an obvious sign of which God is providing the world, but specifically believers, a way for them to be able to tell "this is absolutely it." Matthew 24:29-31, Luke 21:25-28, and Mark 13: 24-27 all state that these celestial and earth shaking signs are to mark the Second coming of Jesus. Comparing this with Revelation, it all adds up.
I like how one brother puts it, and so as not to steal credit, it's Dr. Phil Fernandes, he says it this way about eschatology and I summarize, not an exact quote, "It's vague enough for every generation to think they're end it, but specific enough for the generation of the tribulation to know they're in it."
But let me ask you, why do you think that future generation will be more evil than any previous one? What could they possibly do that is more evil than murdering horribly the innocent Son of God and all the prophets ever sent them? They murdered hundreds of servants of God.
Well that was foretold in prophesy and had to happen to provide reconciliation to the world for those that would receive it through Jesus' sacrifice.
What could the world or a particular generation do that's possibly more evil? Well, in this sense, I'll quote this passage and then comment:
Matthew 18: 1 At that time the disciples came to Jesus, saying, “Who is the greatest in the kingdom of heaven?” 2 And calling to him a child, he put him in the midst of them 3 and said, “Truly, I say to you, unless you turn and become like children, you will never enter the kingdom of heaven. 4 Whoever humbles himself like this child is the greatest in the kingdom of heaven.
5 “Whoever receives one such child in my name receives me, 6 but whoever causes one of these little ones who believe in me to sin, it would be better for him to have a great millstone fastened around his neck and to be drowned in the depth of the sea. (ESV)
So, I'd say the "more evil" thing a generation can do is what we've been doing. We as in a generation, society, culture at large, etc. And yes, the we can and does include compromised, corrupt, theologies and "Christianity." We've been leading people astray, removing the validity of the Bible, watering down the message, corrupting it, diminishing it's integrity and power in favor of a variety of things that lead people into deception and rob them of their potential reconciliation and eternity with God.
What could be "more evil" in the sense of having an eternal, unchangeable, fixed, permanent repercussion for people ?
Deceiving people into an eternity without God on their side because they've become His enemy and an eternity separated from him.
Jesus died, came back to life, and is now at the right hand of God. Those who had a hand in that act and didn't repent likely already came to terms with their mistake and will have to further answer for that in the end just like everyone else.
At least those who had a hand in it, saw the error of their ways, or even those who doubted and hated him (his brother James, for example) had the opportunity to figure out they were wrong, right it, and got themselves on the right path.