i actually raided mythic during night hold in legion, and back then i got a sense of achievement because we spent days wiping on a boss and mastering it before we got rewarded for a kill that felt earned. When i came back in BFA and did normal/heroic raiding. no kills felt earned, because we’d kill a new boss every week, normally after maybe 3 hours wiping on the boss. At which point most of us were still regularly screwing crap up, but we still killed the boss, as the mechanics weren’t punishing, and could be healed through providing you didn’t screw up to many.
Back in TBC/Wotlk/Cata most bosses had WAY WAY less mechanics than they do today. Most of them hit a lot harder though, if you screwed them up. Back in Wotlk if we killed a boss, it was generally because most of us did the very simple mechanics perfectly. That felt rewarding. that felt like we had earned our victory.