This is a different argument then your initial one. With that said tier resets started at the end of TCB due to the problem with feeder guilds not being able to progress past Kara, they introduced badge gear so that casual players could advance.
By WotLK these systems were in full effect.
Furthermore to illustrate the ideas of seasons look at the release of any raid tier and you see people returning from breaks. Once the content is cleared they take another break. Classic servers are a perfect example of this, when MC was cleared people came back to retail if they didn’t pvp, with each raid release people go back to reexperience it and then leave again. That is a clear indication of a seasonal release cycle.
So you are incorrect.