I believe Toxin ignoring both the wielder's Strength and the target's Wounds make it special enough (less special for ranged weapons of course as they all ignore the wielder's Strength). What is so special about not being good at wounding targets with Toughness 6 or 7? It seems to be the exact opposite of what Toxin should thematically do.Generally I think simpler is better. However I feel toxin deserves a special rule, that means something.
I'd much rather remove paired weapons and a half dozen other special rules/traits before giving up on toxin, which S4 seems to do.
Sure I accept the current one struggles to differentiate itself from regular S4, but that's a problem resulting from the 2-3 attempts they had at sorting toxin rule out. Which if I recall yoyo-d between Op and hot trash, before the current workable but meh.. result. Thematically, Toxin is one of the few weapons that should be a counter to normal Hard to wound targets.. the issue here is they replaced wounding against T with well T...
And yes, the history of Toxin explains how we came to the current unsatisfactory result. Which is why I'm quite surprised people seem so attached to it. It's really not something that was well thought-out.