Im a big proponent of the new shard tech. Its made areas that would be insanely laggy otherwise to bearable and actually enjoyable.
Any big event that brings players to the same zones will inevitably cause server lag, but with the sharding tech, it reduces that lag big time, especially in areas where CRZ is activated (aka old zones before Legion). So all the players doing invasions in Westfall and the other zones have A LOT LESS lag now, than they would have had without the tech implemented.
Blizzard once again has proved why they are the best gaming company on planet earth.