You left off Parrots, which are just about as intelligent as Corvids. For example, keas have a similar number of pallial neurons to ravens (or maybe slightly more). Parrots and songbirds generally have extremely high neural density but still lower raw neuron counts compared to primates, which makes their competitiveness in many cognitive tasks interesting.

Among parrots, everyone knows African Greys but cockatoos are also highly intelligent, with goffin's cockatoos the standouts in terms of cleverness.

Also toothed whales. Like, dolphins have developed culture. Probably many more species are very intelligent. Intelligence doesn’t seem too rare.

With more intelligence arrives the tendency for neurotic and compulsive behaviors, frontal cortex or not.