Tbc had 5 with the one boss raids put together.
Wrath had 4 raids if you count the one boss ones together as 1 raid, naxx was just a difficulty slider of the classic version.
Mop had 5 raids
Legion had 5 raids.
Bfa had 5 raids.
Shadowlands and Wod have 3.
Dungeons,
Tbc had 16.
wrath had 14.
Mop had 9.
Wod had 8.
Legion had 14.
Bfa had 11.
Shadowlands 10.
So it would seem raid wise only really shadowlands and Wod are behind tbc/wrath and dungeon wise they all are but legion.
But those aren’t the only actual content in the game so let’s compare added zones to.
Tbc had 1
Wrath had 0.
Mop had 2.
Wod 1 if you want to count a cut launch zone.
Legion 1 arguably 2.
Bfa 2 arguably 3 if revamped dark shore counts.
Then for systems it’s kinda questionable what to count is flying a system or arenas a system? Mounted combat?
Let’s just assume yes those count and exclude scaling difficulty’s.
Tbc had 3. Flying, arenas, daily’s.
Wrath had 2. Mounted combat inscription.
Mop had 3. Challenge modes, brawlers guild scenarios.
Wod had 1, garrisons.
Legion had 3. Artifact weapons mythic+ Invasions.
Bfa had 3. Azerite, islands, warfronts.
Shadowlands 2. Renown, maw.
Depending one what you want to count as systems these could obviously be added to or subtracted from.