Perfect Imbalance

There is certainly a constant shift in power from updates and patches. However meta's are often stagnated by human nature. What I mean by that is that there are viable strategies that players don't learn or even conceive of because they are counter intuitive to the balance of previous game states. Riot has striven to increase the impact and unique playstyle of different champions in more recent seasons in ways that the community has been slow to adjust to.

Fantastic examples of this are Azir's passive, Illoai's E,( and in broader terms her whole kit in general) and the modifications to Darius's Q. Consider that both illaoi and Darius are designed to be more effective the more people they are fighting at once. This is what generally leads players to call them op. In actuality they mistake being broken with being unprecedented. And because of this players have been unable to play around these new strengths.

Consider that for the longest time the best advice players could give to a person consistently losing lane is to demand ganks from the jungler. These champ designs undermine these tried and true conventional strategies. While they are not significant enough to alter the entire meta at a glance, they will take time for the player base to adjust to playing against, because it will take time for people to accept that different from conventional is not the same as overpowered.

Essentially in all things the longer the status quo is maintained the more resistant to alternate variables communities are. Ironically this tends not to be true on an individual basis. I guess people are more likely to believe what others validate them for believing.