I've worked with some phenomenal talent in Kiev. I've also had people who would over-engineer the simplest solution in comical ways, that had to be let go. Not unlike engineers everywhere.
His solution ended up using as many new features as possible, seemingly for the sake of using the new features, but beyond that, it was incomprehensibly complex. Most importantly, it didn't work. It felt like he used the project as an excuse to try new tech and pad his resume.
The entire project was a giant mess of technologies, to the point it looked like every dev who was on it used it to try out some random technology for personal curiosity. I mean... it used multiple RDBMSs, multiple programming languages, multiple formats for transporting information over the network. The set-up/build process was so complicated and fragile. It was insane, this project could have been done for probably 1/4th of the cost of less.
Project management - it's extraordinarily necessary when you have devs who think they are at work to personally entertain themselves rather than build the best product.