AP3 doesn't have "better neural nets" it simply has more compute ability. Solving edge cases such as weather or other anomalous conditions isn't (at least initially) a compute problem, it's a data curation and learning problem as well as a software problem. If AP2.5 could do sunny day FSD and AP3.0 was required for rainy day FSD, we'd have seen sunny day FSD alerady.
People are putting way too much faith in Tesla being able to "compute" their way out of it. There are already far more powerful computers out there (in data centers) that still cannot do autonomy. If compute were the only issue, we'd just have really slow autonomy - like you said in your first sentence, it's about the software.