It's immensely important to involve your users in what you're building, and going multiple weeks without showing a customer what you've built to gather feedback is a great way to build the wrong thing and kill a startup.
It may be fine if you're in a large company, but when your runway is measured in weeks not months, you don't have the luxury of rat holing. Even if you have "months" of runway, it's not generally acceptable to take 1/6th of that to build just one feature, especially if that feature isn't work on as a group, including the customer.
I value engineers that collect feedback every single day from customers, and if a "hard work ethic" means the developer is unwilling to collect iterative feedback, that developer should probably look for a role not on my team.
If you are having engineers talk to customers daily, the value of each of those interactions is likely not very high, or the scope of the work you are doing is transactional in nature. I would be cautious to fall into the trap of thinking the only thing that matters is customer feedback, it doesn't replace product strategy and is often times not the source of innovation. So many products have been built by rumination and coming up with something new, how do you explain Apple, Google, hardware tech companies, etc that release a product once a year? Henry Ford famously said if he had listened to his customers to the fault of everything, he would have delivered to them a faster horse, not a car. Many of the best products are created by solving problems that customers didn't even know they had in new and creative ways.
I would encourage you to keep an open mind and understand that if you want to grow beyond incremental work, you will need engineers that work on longer term projects, and be able to take gambles on work where the idea didn't directly come from a customer. Sure most of them probably won't pan out, but for the few that do, they often times open up entirely new features or product lines that you or your customers didn't even know existed, and are quite rewarding for the team. Every team needs a healthy balance of different kinds of thinkers, it's not something to be angry or resentful about.
It may be fine if you're in a large company, but when your runway is measured in weeks not months, you don't have the luxury of rat holing. Even if you have "months" of runway, it's not generally acceptable to take 1/6th of that to build just one feature, especially if that feature isn't work on as a group, including the customer.
I value engineers that collect feedback every single day from customers, and if a "hard work ethic" means the developer is unwilling to collect iterative feedback, that developer should probably look for a role not on my team.