That isn't the point Christ made. You are totally disregarding the conditions which would accompany Christ's second coming return which were listed in Matthew 16:27, namely, a bodily resurrection that would occur for those who up until then had lost their life for Christ's sake, with rewards given out according to everyone's works, and with the angels accompanying Christ's return on that occasion. None of this happene on the Mount of Transfiguration.
The kingdom of heaven was not established on the Mount of Transfiguration. The kingdom of heaven with Christ enthroned was on His resurrection day ascension to heaven, and it does not "pretty much suck". With the establishment of Christ as our Great High Priest on His resurrection-day ascension, He was given the crown of that high priesthood, and "abolished death" for us, "bringing in everlasting righteousness" as a vicarious covering for our sins. On that day, Satan was cast out of heaven with his angels, and forever lost his ability to be the "accuser the brethren" because of Christ's sacrifice offered in heaven on our behalf.
The destruction of the temple by AD 70 was simply God "taking out the trash" of those dead, "weak and beggarly elements" of a physical temple system, in order to leave the unshaken kingdom of God and the New Covenant / New Jerusalem in the NHNE standing without a rival.
Verily I say unto you, There be some standing here, which shall not taste of death, till they see the Son of man coming in his kingdom.
Elliots commentary:
The immediate sequence of the vision of the Son of Man transfigured from the low estate in which He then lived and moved, into the “excellent glory” which met the gaze of the three disciples
Benson commentary:
Accordingly the disciples saw their Master coming in his kingdom, when they were witnesses of his transfiguration, resurrection, and ascension,
Barnes:
This cannot refer to the end of the world, and there is no need of referring it to the destruction of Jerusalem.
Matthew Poole:
Some understand it of that sight of Christ’s glory which Peter, and James, and John had at Christ’s transfiguration, of which we shall read in the next chapter;
Gills:
To be fair a different interpretation...
nor of the glorious transfiguration of Christ, the account of which immediately follows; when he was seen by Peter, James, and John, persons now present; for that, at most, was but an emblem and a pledge of his future glory: rather, of the appearance of his kingdom, in greater glory and power, upon his resurrection from the dead, and his ascension to heaven; when the Spirit was poured down in an extraordinary manner,
Pulpit:
More in your line of thinking...but not quite...
This advent is doubtless the destruction of Jerusalem, which, as it occurred only some forty years after this time, some of his auditors, apostles and the multitude, would live to behold. This great event was a type of the second advent,
Bengals:
And a previous proof of this matter was given in a week[773] from this time on the Mount of Transfiguration; and, at the same time, out of all the disciples those were chosen who should most especially see it. It is beyond question, that those three[774] who witnessed our Lord’s transfiguration were peculiarly favoured with reference to the subsequent manifestations of His glory.
Cambridge:
” but the meaning in each case is the same. Various solutions are given. The expression is referred to (1) the Transfiguration, (2) the Day of Pentecost, (3) the Fall of Jerusalem.
Expositors:
The words of Jesus about the future provide for two possible alternatives: for a near advent and for an indefinitely postponed advent. His promises naturally contemplate the former; much of His teaching about the kingdom easily fits into the latter.—
Meyers:
understands it as referring to the founding of the church, and particularly to what took place at Pentecost, and that notwithstanding the context and the words εἰσί τινες, etc., which, if this view were adopted, would be entirely out of place (Glass, Calovius). It is likewise to explain it away in a manner no less arbitrary, to understand the passage in the sense of a figurative coming in the destruction of Jerusalem...
The above
commentary refereces can be found here.