Here's the problem with being honest in an exit interview: any given fact can be interpreted in at least two ways, and the circumstances of an exit interview (you're leaving and have in effect said you don't like working there any more or aren't up to working there any more) can sway your CEO to use the interpretation that will not achieve your wants (an easier life for your colleagues) and may hurt you in future. This is true whether you make entirely neutral fact based statements, or provide value judgements and give opinions.
Example: "I was really overworked" or "deadlines were routinely set too tight" or "[person] did not manage our team deadlines well." You think you're giving important information about process and expectations. But it's easier to interpret as "Marche101 wasn't able to work at the pace we require."
Eventually, when a steady stream of people who appeared in the hiring interviews to be able to work at an industry-appropriate pace continue to leave and make the same claim in their exit interviews, the other interpretation will kind of force itself on the CEO. But you have no idea how long that will take and in the meantime, the CEO remembers you as the one who couldn't work at an appropriate pace.
So is there no room for honesty? Some would say no. I would say to sow a seed for the day the CEO is ready. So don't draw conclusions or offer advice, or say any sentences that start with I. If you can, don't offer anything until you are asked. Some exit interviews will ask "is there someone here that you had particular trouble working with?" or "if you could have changed one thing about this job, what would it be and would that have been enough for you to stay?" Rarely do they ask "why are you leaving?" directly.
If you're not asked a specific question, just for "any advice or things you'd like us to know?" you really need to tread carefully. Perhaps "the work pace leading up to deadlines is not what it is in other firms" or "the process around scheduling here is unusual and I'm not sure it's the best it could be." A CEO who is interested and wants to make things better will ask more questions; one who has written you off already will thank you for sharing and move on to the next item on the exit interview checklist. By not saying anything super memorable before you know it will be well-received, you lower the chances of leaving a bad impression.
