Old WoW had patches with new raids and new, stronger gear, but it did not have seasons, and was distinct from what we have now.
Seasonal WoW: We have different tracks of gear (from explorer-track through myth-track), which are earned in progressively more difficult content, and each track has its own range of potential item levels. However, when the new season begins, we have, effectively, all-new tracks of gear. Season 2 explorer gear isn’t the same, item level-wise, as Season 1 explorer gear. Each new season raises the gear level ceiling, but it ALSO raises the gear level floor. By the last season of an expansion, world quests are giving you gear that is objectively stronger than Season 1 raiding gear, while the raid that was “current” in Season 1 is still giving you that old gear, which cannot be upgraded and which is weaker than easier-to-acquire gear of the current season.
Traditional WoW: Every new raid offers progressively higher item-level gear, increasing the iLevel ceiling with every major patch. However, gear acquired from world drops, from quests, from dungeons, and from earlier raids remains the iLevel it was on expansion release. Doing a run of the Steamvault while Black Temple is the current raid doesn’t reward you any different loot from doing a run of the Steamvault while Sunwell Plateau is the current raid. Likewise, if your guild was going slower or you missed the early expansion, you’re not immediately jumping into Sunwell Plateau because you’re not geared for it. The way you gear for it is by running Black Temple (and the way you gear for that is running Hyjal, and the way you gear for that is by running Tempest Keep, and the way you gear for that is running Karazhan, etc)
There are positives and negatives to both. Traditional WoW was, obviously, MUCH less alt-friendly, whereas the newer seasonal WoW is very friendly to alts by comparison. On the other hand, seasonal WoW tosses raids in the trash the second the new season starts, effectively shrinking the expansion and severely limiting total amount of content.
I think, in a perfect world for me, we would retain the alt-friendly seasonal nature of current WoW (increasing the iLevel ceiling AND floor), but maybe retain access to old raids throughout the expansion as valid forms of content and gearing. I wouldn’t want “last season” raids replacing “current season” raids as the cutting edge gearing content, though, so it would have to be balanced somehow.