IMO, your boss missed an opportunity. He could have still tried to compete in that market - heck, some competition is good for you, and in the later stages a prereq for mainstream acceptance.
It’s healthy to assume other folks already have the same idea as you. You just need to understand the customer pain points better and execute better. Hey, even 2nd place competitors can drive ideas forward and end up with market share.
Actually, stealth startups generally don’t get to test for product-market fit, which means they’re often leagues behind the folks doing it out in the open. The advice I always hear is just to get it out there and start testing.
We all get misses sometimes, in entrepreneurship or otherwise. The only danger is if that dissuades you from trying again. Good luck!
Ultimately you need to choose the right option for yourself, no one else can tell you what that would be.
Some folks thrive in situations where they are working out of discipline. Some folks succeed as long as they have something to look forward to further in the journey. Other folks will quickly burn out if they’re working long hours on something they don’t engage deeply with.
Each of these approaches have their own strengths, it’s just a matter of learning about yourself and where your preferences & abilities are.