I write resumes for a living (yes, that's a thing) and have advised many HN'ers on career topics. When you're working by yourself you generally don't have any useful point of comparison as to 'how good' you are, and perhaps more importantly, you don't have anyone to learn from. Both are potential problems.
The best way to get some feedback on how senior you actually are is to do some interviews - practice interviews and interviewing.io is one way to do so in a no-risk setting, and the feedback you'll get will give you some ideas on things to brush up on.
As for long-term career, if you've managed to take home a paycheck for 10 years as an engineer you must be doing at least some things right. Finding a role with a team that truly invests in their employees and finding a mentor might be useful. In your case I wouldn't accept any job where you're the most senior person - if there is nobody at the company better than you, find another company.
The best way to get some feedback on how senior you actually are is to do some interviews - practice interviews and interviewing.io is one way to do so in a no-risk setting, and the feedback you'll get will give you some ideas on things to brush up on.
As for long-term career, if you've managed to take home a paycheck for 10 years as an engineer you must be doing at least some things right. Finding a role with a team that truly invests in their employees and finding a mentor might be useful. In your case I wouldn't accept any job where you're the most senior person - if there is nobody at the company better than you, find another company.