Hi, there are two parts to your question: one syntactical, the other interpretative.
On the syntactical question, it looks like you are construing ὥστε as either:
(in your first reading) introducing a clause of comparison (‘just as’), or
(in your second reading) introducing a new sentence of result (‘so’).
The second reading is right; the first isn’t (ὥσπερ or another relative adverb of manner introducing a clause of comparison such as ὡς, καθάπερ etc. would be needed instead): have a look at e.g. sec. 50.37 of the Cambridge grammar, or the LSJ entry on ὥστε.
On the interpretative question (e.g. whether he is providing another argument etc.), if you’re reading 2.19, I’m sure you know this chapter is a minefield. There are many different interpretations. Check out e.g. David Bronstein’s 2018 study of the An. Post. (he was nice enough to share a pre-publication draft with me and to talk through some of the issues in Aristotle’s complex work):
You may find chapter 13 The Origin and Aim of APo 2.19 especially interesting. Also check out the other recent studies on An. Post.: if you are venturing into these murky waters, best to take a couple of maps at a minimum.
Seems to me that the OP ’s second reading of the syntax (“so too”) is as wrong as his first, on account of the “too,” as if he understood it as “likewise.” Neither of them renders ὥστε, a simple consecutive clause.
But I’m not about to wander into the hardcore logical minefield, where I’d quickly be blown to pieces.