I think the problem is people often confuse non-punitive approaches to parenting with "soft parenting".
Non-punitive parenting doesn't use time-out in a punitive way and the belief is that punishing children for misbehaviour isn't very effective.
HOWEVER, done properly, the approach is NOT permissive and definitely does believe in setting and enforcing boundaries. And it does involve being very firm, but kind. (Not a million miles from 9to5's approach, by the sound of it).
Long lectures are indeed useless on children, at whatever age. But having a conversation about a situation (where the child contributes) can be one useful approach (after everyone's calmed down).
I think it's difficult not to "allow" a tantrum as, with the best will in the world, not all tantrums can be avoided. Also, ignoring the behaviour in a calm way can be very effective. Eventually, most children run out of steam and also learn that all the screaming and thrashing about won't get them what they want or be rewarded by attention. Sometimes you just have to bodily remove them from the situation, though and let them calm down somewhere else, depends what's going on at the time!
It's a tricky and fascinating area.