If you genuinely believe that a giant mass of players doesn't cause the servers to lag up, I have a simple response for that: Ruin shards during the Nazjatar PvP event. That community would flood shards so hard, they'd become nigh-unplayable. While part of me does pine for the days where sharding wasn't a thing, there are perfectly valid technical reasons for it to exist, particularly around expansion launches, which have been smooth for the most part the past couple of xpacs.