Hardly evidence for anything, it was gross missplay.
Anyway, the issue of the slayers is the same, they're fragile and expensive. I'd say they are worse in ToW because they can be pushed back after losing a round of combat and thus you're not even certain to block what you can get your hands on.
Playing a big (like 15+) unit in a marching column means you can't even charge and as they arent drilled you're going to lose a turn redressing rank. I think it's only good-ish as redirection, but again you dont want a big unit and wouldn't a unit of warriors do exactly the same anyway?
Thinking you can kill monsters with them is wishful thinking - not only are they actually not good at killing armoured monsters, but by all means good players won't let a m3 unit get in contact with their monsters, at least not reliably.