In Europe, the so-called "Balance of Powers" system existed for a long time, until 1989 when USSR, the last major European power, effectively began to collapse.
However, in Asia, that kind of concept does not exist. In East Asia, it was China lording over all the countries around it, except Japan which was separated by a sea and didn't really begin to become China's rival until much later.
There has been quite a few KPop Rivalries, but in the end, all of them ended with one completely shadowing another.
The SNSD-Kara rivalry in Japan lasted 2009-early 2011, when Kara effectively self-imploded following the contract issue. (Yes, I have been in Kpop long enough to remember that.)
The SNSD - Wonder Girls rivalry ended in late 2011 when SNSD cleaned WG's clock (although WG did have the last laugh on 2016 by defeating GFriend in the end; GFriend was made on the image of SNSD).
Speaking about that, the Twice-GFriend rivalry lasted for early 2016 but by early 2017 GFriend also began to implode.
Big Bang was not really competing against the SM acts TVXQ (later DBSK) and Super Junior; their targets were different.
I do not follow K-hiphop too much so I won't mention the rivalries in there, and these acts are not that really popular among i-fans anyways since they have their own hip hop acts to follow.
The biggest rivalry in KPop in the KPop era appears to be either the SNSD-Wonder Girls Rivalry or , for the recent memory,
I am not going to recount all these incidents of the EXO-BTS rivalry. It suffices to say that this rivalry, which began in around 2016, was ended by end of 2017 and we all know who won.
In conclusion, I do think that KPop rivalries do not last for more than 2 years because by 2 years the victor and the vanquished would be apparent. Because the KPop market is so competitive, rivalries can't really last for too long in there
