You seem to be saying that the project is not moving forward quickly enough because the developer doesn't work enough.
Are you sure the management / communication / teamwork is not the problem ? You may be setting expectations at the level that cannot be reached with your current team and management. Maybe you should set easier targets so that everybody stays motivated after reaching said targets.
Problems are everywhere as in every other company. We have flat hierarchy, no middle management and almost nobody above developers. They do all technical decisions and decide how to implement features. Features are selected by Product board and developers have little influence here.
That might be a core problem right there. There's no developer influence in product meetings? While on the business end there might be a need for a feature, business people are not going to understanding what complexities are involved in a particular feature. What you might think takes a day could take 3 weeks. On the other hand, you may be passing over useful features you think are complex but only take a day. If you trust your developers with as much as you say you do, they should have a voice in your meetings. That may be a way to retain this lead developers interest
Are you sure the management / communication / teamwork is not the problem ? You may be setting expectations at the level that cannot be reached with your current team and management. Maybe you should set easier targets so that everybody stays motivated after reaching said targets.