I think that bringing a deck that you have the skill to pilot is another factor entirely. It is actually probably the single most important factor in choosing a deck, but it’s not the only factor. Trying to play up variance is simply another one.
Just because you should bring a deck you’re competent at piloting doesn’t mean that playing towards a variance spike isn’t reasonable in situations where you could reasonably bring one of two decks. Bringing a deck which a lack of skill can be offset by good luck, like NEH AstroBiotics, isn’t the only option. Perhaps your win rate with Kate and with Big Dig Combo Maxx are both around 50%. Some decks like 7-Point CI, Big Dig Combo Maxx, and to some degree, Butchershop aren’t necessarily super high variance within a game, but have matchups or certain cards that just wreck you, and one way to play up variance would be to play this sort of deck and hope your more skilled opponents don’t draw or aren’t packing the sort of disruption or protection they need to beat you.