There's something in this, though I'm not convinced it's that lead gen replaces sales. If anything, buying cycles are getting longer.
In many sectors-services, B2B, high-ticket products-asking for a direct sale straight off the bat is increasingly difficult. Capturing a lead, nurturing the relationship, then converting... that can actually build more sustainable revenue.
That said, it really depends on the business. For a £20 impulse buy, slapping a lead form in front of someone just creates unnecessary friction.
I've also seen lead gen campaigns outperform simply because they optimise for a lower-friction action. But if the quality behind those leads is weak, that apparent stability is misleading.
So yes, sometimes a lead gen campaign is just a sales campaign in disguise. But ultimately, what matters is cost per real customer-not cost per lead. That's usually where the answer shifts.