Nature Structures

I'll repeat myself. It seems that VD is only good for neutrals and units of levels 1, 2, and 3, but against leveled-up heroes and level 4 units, they seem somewhat lackluster — sometimes it feels like they're just cannon fodder (unless there are dozens of them and they trample the unfortunate hero underfoot).

Of course, let's say they won't work against a pumped-up Barbarian. But still, against others, he is not weak. Firstly, he has direct damage spells, which are much-needed help for Nature magic. Secondly, again, confusion, which can slow down the attack of a level 4 unit.
Essentially, in battle, VD deals with units. It can of course affect the hero as well. But for a specific showdown with an enemy hero — the Bard can summon the same praying mantis!