And a bad businessman at that.

Aye, but a lot of the current day versions of those IP's have also been done without him now, especially with new concept artists putting in their own adaptations (like the DR 1-2 Remasters, which ended up changing character facial designs and even voices).

Take for example, crediting the og artist for Sonic. Yeah we can still give kudos, but if they aren't currently designing modern day concepts/designs for modern day Sonic, then that credit should go to the ones making the current iterations that people like/dislike. 

Frank Klep made half if not most of the OST for the og C&C games, but to put this into the same example, he's still doing music for RTS games, just not with EA. What Kenji is doing is copying what originally worked for him at Capcom, but that isn't entirely what people wanted, and he ended up falling short. Meanwhile with Frank Klep, all we want is his guitar riffs and electronic keytar humming in the background, because he's naturally good at what he does.

For some reason Kenji just isn't. Ever since he left his career has been well, not great, not making big bangers or anything truly noteworthy, not like other Japanese creators/devs/directors are putting out (Like Kojima for example). 

Because, as said above, he's not a creator. Kamiya should know he worked at Capcom. A lot of former Capcom talent turned out fine. Street Fighter vets of II left and created Fatal Fury. Kamiya left and Bayonetta—wonderful 101. Mikami left and got VanQuish. Evil Within. Hi-Fi Rush. Ghostwire. Plenty of Strider team left, and we got some good clones. Like Osman and Run Saber. Since he left Capcom he was exposed, that he really needed the talent at Capcom. Much like Itagaki needed the staff at Team Ninja more than they needed him.

There is always this element among artistic industries (and really any skill-based industries) that have a bureaucracy. People who get a lot of credit for being professionally polite glory hogs. A lot of where the credit goes is ass-backwards. Unfortunately, politeness and ambition tends to count for a whole lot more in bureaucracy than actual creative talent - and in a bureaucracy, those in power can take undue credit without much criticism, at least until they’re exposed in some way.

Sometimes people get undeserved credit thrust on them because they created the initial concept even though the real talent and direction came from others. Simpsons is a great example. While the initial concept and Simpsons family came from Groening, James L Brooks created the general direction and was the one who initially prompted Groening to pitch something in the first place (to replace a concept Groening didn’t want to sell), and Sam Simon built most of the early Springfield universe and character personas, with Al Jean kind of taking over both Brooks and Simon’s roles, later.

That's the point. He is never intended to stay with a project as a developer. His main role was a producer(where he just makes sure project remains on track). Inafune is NOT a developer. He creates concepts that his chosen teams expand on with him just checking in. He should not take ALL the credit but he is entitled to some it.