Right? Tamamori is great, his conflicts are all so very human and relatable, he really carries the story as the main character well. And as the Kawase shill I am, I feel obliged to tell you his route is definitely worth more than just an extra (but yeah, it is weaker than Minakami's route, I have to admit) so hope you find it worth your time when you get around to it~ Unfortunately, the other three are just that, extras, yeah.
As for myself, I'm slowly going through 428 and man, what a fun ride! The multiple protagonists thing and the very intertwined plot lines sounded confusing at first but it's actually pretty funny and rewarding to navigate on your own. The wackier the better, so I just can't not like Tama's and Minorikawa's antics and how much "destructive" for the others simple shit they pull can be (specially Minorikawa, guy can be really chaotic).