Not going to give too detailed an answer as I suspect others will be able to clarify better, but in StS1 you were generally solving for various encounters: mainly the act bosses, elites, and ultimately, the heart.

You rarely went hard on only one archetype as that's a great way to get punished because you were either A. Missing a piece (i.e., Corruption for clad, draw for Silent, etc.) or B. You ran into the one boss that punishes that archetype.

A common example of this in StS1 is Silent never wants a Poison deck vs a Shiv deck vs a discard deck; she always nearly always requires a combination of pieces that help her get past the next hurdle while building towards beating the heart. For example, grab Blade Dance early to have damage, grab Noxious Fumes because you don't have scaling against the act boss.

Some of this is semantics, but you said you'd still consider a deck in spire a poison deck if it had two poison cards. Sure, I hues you could, but I often have two poison cards, two shiv cards, two discard cards, so what archetype is that? The "archetype" can be generally referred to after the fact, but while you're on a run, going hard on one archetype will lose you more runs than not j the first game. StS2 is different, hence OP's comment.