No, this is not a natural cycle. Natural meta cycles happen usually when new items are indroduced. After the introduction of cinderhulk meta naturally changed into a tank one because of how good the item was.
It would have been ok if the item itself had been tweaked at that moment.
However, this was not the case. Most of the cinderhulk users (Sejuani is the best example) got nerfed because of how strong the item was. Then the item itself was nerfed, but the champion nerfs werent reverted.
This wasnt a natural change in meta. Some tanks were straight up gutted with 2 waves of nerfs (cindehulk and theirs).
When sated came, meta changed again, however, even after meta changes you can usually still see the lingering effects of the older metas, some champions which still do realy good. However, in this case it didnt happen. Like i said before the double waves of nefs fcked up a lot of champions.
This is a new cycle, but its definetly not natural one, it was tampered with, even before it came out.
Also, while vayne wasnt the "best" adc for the job all this time. She was still played a lot and reliably. Unlike some, she actually saw LCS and other championship plays. Champions like varus were invisible until this new adc mid meta.
Also, while she didnt really receive buffs to her, she isnt in a vaccum, she is in a champion community. Cinderhulk meta is over, that should logically mean that she should not be in the meta anymore? Right?
But lets look the other way. After the cinderhulk meta which made her popular, people found out that she is just as good if not better against squishies than tanks. Something simmilar happened to corki and trinity builds which were overlooked for a long time.
Then, we have some other adcs being nerfed and at the same time, botrk, gets buffed on its passive part which is really important for vayne.
Vayne should have fallen out of grace after cindehulk meta if you think logically. Yet she became even more popular after the meta she logically should have been best in. There is a problem here. A tank buster, is one of the best adcs in a squishy sated meta.
EDIT: In the end, all i want from riot, is consistency. If they do something like this with vayne, they should do the same with cindehulk disabled veterans. If they buff someone like lee for not seeing so much average play, why are they nerfing someone like azir for the same reason?
I want changes, to make logical sense, and them to be consistent with every change.