What can I say... It's an objective.
Giving advantage is what it is supposed to do, like all objectives. Towers, buffs, epic monsters, inhibitors... All contribute to snowballing.
Some, like infernal Drake, go often unnoticed, so that you can't track the lost fight and tower directly to it, but their contribution may be even higher than herald.
With infernal, you haven't any agency, it's there, and the enemy team will be empowered until the game ends.
The reason why I like herald is because it is an objective advantage that can be countered and managed. Yes, of course it will do some damage, of course it's a lose-lose situation for you, but the extent of the lead the enemy team may get depends strongly on their and YOURS decision-making.
He may be overtuned right now maybe, but i support the concept behind it. I'd rather have herald than Drakes, to be honest, for I think it is an healthier form of advantage that forces decision making from both teams.