Wave of Wrath vs. Vapor Blade
Vapor blade is narrow and it can have problems when bumping into debris on the ground.
Guardian also has https://wiki.guildwars2.com/wiki/Permeating_Wrath to help with potentially tagging more mobs.
You could also add in sigil of blight/fire/torment but it is probably not worth it unless you already happen to have a weapon that have these upgrades in them.
Vapor Blade definitely is nothing like Wave of Wrath. Its a straight-up projectile and as such hits basically in a straight line. Its got the range, but it lacks the AoE.
Wave of Wrath is pretty unique. There’s really not another auto-attack in the game that hits a wide area AND hits at the same distance like Wave does.
If you’re looking specifically at Elementalist, your best bet is probably either Lightning Whip (Dagger #1 in Air) or Chain Lightning (Staff #1 in Air). Lightning Whip only has something like 300 range but covers a fairly good arc around you and hits twice. If you can keep up with / ahead of the zerg enough to get into melee range with mobs it’ll do the trick for tagging. Chain Lightning has a lot more range and will bounce to additional targets, but it does require you to constantly retarget new enemies ahead of the zerg, so its more “active” than Lightning Whip (which you can basically just hold down 1 and run towards enemies). Either way, if you have Tempest you can also throw in an Air Overload for larger groups to tag lots of them.