Arrogant or not, we wouldn't have gotten Yakuza, Judgement, or Binary Domain without him. As to how much of his leadership of the studio and initial concepts factored into the final products being great, it's hard to say. I do enjoy the Yakuza games a lot more before they became Like a Dragon (around when he left). The old ones felt like Japanese crime films with a bit of that wacky Takashi Miike edge but the new ones feel like comedy anime.
We'll see if Nagoshi manages to pull a Kojima with his old pals or turns out to just be another Tomonobu Itagaki or Yu Suzuki without a well oiled team. And we'll see if RGG has any good concepts for new games that are not LAD.