Considering this arcade racer was made by Bandai Namco I think they did a great job once you take the time to realize that Bandai Namco doesn't have the rights to make the Diamond City track any more of a reference than it already is. If Namco had more access to the IP I'm sure they would have done a much better job. Seeing as this is their first stab at anything Wario related at all and despite the actual track being generic I think the assets and references in this track outdo any of the other tracks in this game that aren't copies of tracks from prior in the kart series. The mario arcade games don't have very intricate/original tracks to begin with. (again because they were made by a company that doesn't have as many rights as every other maker of mario kart games which are mostly nintendo themselves or at least have nintendo on the developement team).
They definitely did give a damn and went ham on custom models but their hands were clearly tied by what is and what isn't copywritten and trademarked by Nintendo.
I know this is 9ish years later so its kind of a gimme at this point but Nintendo has always been notorious with giving companies rights to make them a game but none of the rights to anything actually related to the game. Usually Nintendo wants to charge companies like Namco way too much for assets/likenesses that aren't worth the money they would pay Nintendo just to make Nintendo more money with a game. Think like when a shark in shark tank tells someone they will invest but want 8x money back and royalties forever. Its just not worth it 9 times out of 10.
Like if you think Nintendo is stingy/greedy with how they legally pursue FAN GAMES that make NO MONEY, imagine how hardcore of a slice of the action they want from people actually doing real business negotiations with them. They have been sued, created rivals, and literally LOST IPs because of these practices. Nintendo has also been shown to hold grudges. Example; Held a grudge against Universal Studios for 20 years for US protecting their IPs while simultaneously trying to sue the creators of Game Genie (despite them having even less of a case than Universal had)/
tl;dr: Nintendo is two-faced and unfair about their IPs, it makes sense that Namco wasn't able to do more with this track, and they definitely gave it their all design-wise considering working with Nintendo must truly suck and most people who work for nintendo complain that management sucks
https://www.glassdoor.com/Reviews/Nintendo-of-America-Reviews-E4173.htm. Namco did all they could with their hands tied.
