Physical healers are pretty much Guan Yu and they already showed aren't willing to have an item that's only beneficial for one character by reworking Gauntlet of Thebes. Asclepius hasn't been bought lately so it's not all that antihealing is making such an impact even against Asclepius as you say, that got recently buffed.
Antihealing items usually aren't the best to get just for the sake of getting more antihealing. Except for maybe Brawler's, they don't provide stats that attractive so you consider the antihealing part as just a little add-on to be more of an annoyance even if you don't need it. Divine Ruin is OK, but if you don't really need the antihealing, there are items with way more power, pen or CD such as Spear of Desolation, and with the cost increase of Pestilence I don't think they keep buying it just for the stats. A character like Freya is never going to build as much antihealing as they can just to bother because there are much better items out of there for them.
The current stats of Toxic Blade are too ambiguous. Common sense tells this item is for offensive basic-attack focused characters, but the stats don't match this concept. I'm talking of a change in a way the item makes sense, not to break it. I maybe made a vague suggestion, but I think I made pretty clear it was just to get it purely offensive and all current stats would be subject of shift and balance as offset.
Cursed Ankh is not really bought at all unless it's heavily needed.
A right change for this item wouldn't be the end of healers, just a more solid option for those gods that can't rely on other antihealing items. If they didn't really want TB to be viable for the reason you mentioned, then they simply shouldn't have released it.
Nevertheless and regardlessly of Toxic Blade's state, I do think that antihealing should have some sort of limit or diminishing return effect. Items shouldn't have the power of completely negating a character's gimmick. They already removed the former Stone of Gaia's passive for that very reason and reworked Asclepius making clear that they wanted to fuel combat healing, but the way they treat antihealing items contradicts it as it encourages out-of-combat healing.
They have to tweak this, but also TB's core stats.