So, a lot of the recent attention is on bifacial east-west arrays because they produce a complementary duck curve throughout the day. In that case, pure vertical makes sense, and production just takes a dip at local solar noon and recovers soon after.

But for traditional south-facing panels, I'd argue that straight vertical is still optimal, at least for higher latitudes. Vertical panels are extremely good at shedding snow. They produce more in winter when you need every watt you can get, and less in summer when the sun is high in the sky and you don't need all that extra power anyway. As soon as you tilt the panels to minimize cosine loss, you open yourself up to snow buildup which can dwarf any cosine gains.