It wasn't fear of damage creep. It was fear of this being too much power.
I want Q+E AP scaling to actually be good and I want Q max to be good (it's currently his worst max and what most players in low MMR do).
Your "obvious" max being bad is a really, bad thing IMO. There used to be a more complicated changelist, but I pared it down over worries of the message getting lost.
Ultimately, Q and E have cooldown incentives, plus the increased Q damage on rank-up, so with the base damage functionally getting increased via soul scaling, that should help those being worth the points.
Lantern nerf is mostly because of concerns of too much power, though again, I'd rather reshape the abilities somewhat to make Q>E>W a generically good skill order, which it currently isn't.
Anyways, circling back to Thresh in the first place, I think he's mostly a damage champion. Making him threatening against no-peel bot lanes is important and hopefully that is true with these changes.