I have never seen such statistics. Based upon my personal (small) sample size, it would seem that it's better than 50% for people who submit a credible response - CIC knows this is a swamp and thus they try very hard to avoid getting into it.
The Companioni decision established that insurance could be used as an important factor for mitigation (though in their specific case they didn't have the insurance yet and thus the plan was "inchoate"). I presented 100% coverage (two employer provided plans, one of which was a PHSP that is a non-discretionary health savings plan that pays any medical expense as defined by CRA, and one private plan - that was paid for via the PHSP) with a total coverage level of ~$68k and was still refused. Then again, when we challenged in Federal Court the court granted the application for leave (which means they agreed to hear the case) and the medical officer was left making up post facto explanations for why she ignored the insurance entirely ("I was not convinced that it would cover in this case"). That's probably why my second application was granted so quickly.
I worked with an attorney who indicated to me that he routinely was able to assist people in obtaining a reconsideration of a fairness letter. Indeed, he was shocked when I was refused, as I had an extremely strong mitigation plan.
From what you've said you do have a strong case. You should submit it. But if you want to reserve the ability to challenge a negative decision, I'd suggest working with an attorney specializing in excessive demand medical inadmissibility because they can also frame information that would be suitable for legal arguments.
If you have 100% employer funded insurance and sign off on the declaration of ability and intent there is no reason for them not to find you admissible.