99% of apps never need to shard data. Probably closer to 99.9% if they are single tenant.

That seems off in my experience, but maybe it's different in different industries.

Either way, working around sharding and scale seems like a place where a good AI could help provide recommendations and tradeoffs, so it's disappointing that the model doesn't seem to deal with it well. For basic relational schema design, I don't see much benefit of having AI.