I don't play TBC Classic but I have done the TBC timewalking. And I can say the biggest difference between then and now is that mobs will actually affect CC attacks against your group. Group members will be sheeped, hexed, or silenced. Tanks will be gouged and lose aggro as the mobs attack the top dps. You'll be counterspelled and have your magic school locked out. One time my group wiped, I think it was in Mana Tombs, and the group was all mad at me, the healer. I asked them what they expected with them having pull four packs each with mobs with silences who kept me permanently silenced for over 30 seconds until we were dead. Another time I was kicked from a group after we wiped on the first boss in Mana Tombs. I warned them that all the trash in the room would pull with the boss and they called me a liar, that no such mechanic exists. And when I warned them about his damage reflect shield they ignored that too.