If your team cannot wait to leave at 6 you have a problem, but if you send your team home at 6 because they worked efficiently and achieved something, that's some work life balance then.
Don't just copy what they do. You have to focus on your own development and should try to not mimic theirs. You don't know their plans and running after them will distract you from your own way. It might be just your impression that they are faster or whatever, since you know all the details in the field. Sure, you can emulate some good points at the moment, but keep focusing on an overall strategy that has no room for them, too.
I've been in that situation, too. I got out of it by us selling the company.
You should get rid of your co-founder and step up to be CEO yourself and start looking for someone who will do good work. Your co-founder might not have the incentive like you do, so maybe he feels fine with being average. There is no way to change such a person.