I dont know enough about his work to know if his style is what I would want for D&D moving forward.
As a co writer hard to know what parts are his and what parts were others.
I know them from freelance work before most of the things listed here. It doesn't really boil down like that with freelance work very often. You're not deciding the tone or the flavor, but mainly fleshing that out for the publisher.
I've been one of those coauthors when we were both freelancing for 3PP D&D companies. Maybe PF as well, though I don't clearly recall sharing a credit on anything prior to D&D 5E.
The way it typically works is that there's very little interaction between the freelancers on the actual work. There was a lot more of that at one point, but then it seemed like publishers further compartmentalized and siloed off various sections of jobs. So you're often given a chunk to manage and write, and that might be anything from "give me a chapter on this part of the map," to "Magic shoes, 1k words, if you're up for it," to "here's a list of monsters to make," or even "here's a list of monsters, and here are a bunch of details on the mechanical specifics." In that kind of a setting, you interact more via socials or (further back) on a company forum.
Anyway, I can't say I know them well at all, but I've worked on several of the same books. We're friends on socials, but I've had only limited interaction, which isn't unusual. I'm far chattier with people I've actually been in rooms with or know from personal life outside of work.
That said, I know enough to say that they're good at the job. Joey Haeck is a good writer, gets it done and done well, and I have never heard a single bad thing about them, either personally or professionally. If I were still a big D&D guy, I would consider this very good news because they're up for it, I know they care about it, have a good attitude, and it's all they want to do. Frankly, they're lucky to have them.
I mean, that's not a job that entails running the ship, but I'd say you're in safe hands.
I think people sometimes don't like the direction of a book, and it's not unreasonable to think "this writer must suck," because they don't realize that the person doing the writing didn't decide on that direction. That's particularly been a problem with D&D for a long time, in my opinion. They've hired some really great, talented people... and then gave them crappy assignments, stifled the creativity they hired them for in favor of rehashing the same old material over and over with a new coat of paint, and they do what they can with it. Then they hit a wall or slow down for a minute, and they lay them off at the next quarter and declare a "new direction."