Melee champions 1 shot Zyra's ulted plants?

I find this completely counter intuitive that I can spawn plants, ult them so they get more HP (and attack speed), but they still get 1 shot by a melee champion.

Maybe it was 2 autos and I just didn't see them, but this just seems like a nerf to Zyra (mid or support) if her ulted plants just instantly die regardless of the extra health they have. I understand that if left alone they now last longer in general, but dying so easily when they are supposed to be buffed seems off.