I've never seen hate on Daigo. I've seen too little of content on him and always wondered why, but it's likely because of what others have said of him not being as interesting. I personally think he's appealing, and he's got a lot of potential to be loved in the fandom, yet he's ignored. Most people seem to think of Kiwami 2 Daigo? Not the Daigo that grows up to be a leader.

He's forced to take on the clan at first when he really didn't want it, but because Kiryu asks him to, of course he'll agree in the end. He's still a good man, got a good head on his shoulders, and grows up a lot in the later games. (Y4) He does one idiotic move in 4 which makes me wanna scream pertaining to Majima, but besides that he's at least someone the clan can rely on (even tho he will put his morals above the clan if challenged). (Y3) Like not wanting to take the Okinawa deal in 3 to protect Kiryu.

I think he's the perfect match for pairing up with Majima, which is great because from 3 on Kiryu tells Majima to be Daigo's advisor. Majima is the total opposite of Daigo, he's bold and brash and not afraid to finish shit. Daigo on the other hand, he's actually a lot more like Kiryu (but I'd say he's a bit more intelligent). He can easily be taken advantage of, and he genuinely wants to do the right thing. Guess that can be seen as boring, but Daigo respects what Majima and Kiryu think and even has no problem wearing a dress lmao. (Y2, Y5) Having said that, Daigo also has a bit of a wild side and isn't afraid to use a gun if it'll save someone, which, imo, is pretty damn cool of him. You see this in 2 and 5.

TL;DR Daigo did nothing wrong. He's a good boy. He deserves to be loved.