I think there many problems in S3 dev.
First, of course, the budget. Let's remember that Shenmue 3 had roughly the same budget as the first Yakuza. A game that is 15 years younger, and way less detailed and way smaller in scale compared to Shenmue 3.
There was of course a very short dev time for such a game. Especially when you are mounting a brand new team. Usually, when you mount a new team, you spend a few months on internal projects, that you will never release, but just so the team can get used to each other, used to the tools etc... So yeah, too little time to create such a game with such scale.
Also, I've heard that creating an old style kind of game is harder than we think. Because todays tools and engine are made to be very practical about current and modern gaming, but if you want to have an old school feel, you have to put in a little more work (I've heard that, but cannot say 100% if it's true).
And also "poor management". I'm not saying this like Yu Suzuki is a bad manager per se, but obviously, when you didn't have to carry and manage such a big project for 15 years, it's hard to get back on the job, especially when the gaming industry and gaming tools evolved so so much. So Probably that Yu Suzuki was lost at first when trying to give a direction, because he had to find the time to get up to date.
And with all that, they still delivered a game that I consider good and more than decent and that felt very special.
So now, I'm sure that Yu and his team learned from the mistakes they made during Shenmue 3, and they have alot of stuff, features and mechanics already developed that can be reutilised and reworked a bit.
If they are given a proper budget and enough time, I'm sure that Shenmue 4 will be a very great game.