He was mostly exaggerating. The intended use-case scenario is pretty obvious: it's called 'The Culling' and killing a target with it allows you to use Relentless Pursuit to catch up to targets, so it's reasonable to assume that Zenon wanted players to use it to gun down low-health targets escaping from a team fight in a Vayne-style clean-up pursuit.
And that's fine, but as a designer you sometimes have to accept that players find innovative or at least more practical uses for the things you create. The potentially very low cooldown makes it a useful sieging tool, and in general most players would prefer to use their ultimate for a relatively small amount of "safe" damage in the course of a team fight than for an easier clean-up after the team fight. That's the case with most 'execution' ultimates, really: winning the fight is more important than having a super-clean mop-up in the aftermath, so players will always prefer to use them earlier than their "optimal" designed conditions.
I mean, Ace in the Hole is similar - it's really just meant to clean-up a kill on an enemy escaping a fight, and is almost always a loss of DPS if used mid-fight - but players who use it as a harassment tool aren't wrong, they've just found a use for it outside of the intended design parameters that's potentially better.