Nos, I think it translates roughly to:
Type I diabetic failed MCA medical, but believes it is not justified. [I could be persuaded to agree, however bearing in mind it would also fail an LGV, PCV or Commercial Aviation medical, I doubt he will convince the MCA that taking passengers to sea as potentially the only 'competent' person on board is an acceptable risk.]
He reinforces his argument by asserting the "diabetics have sailed round the world (e.g. on Clipper round the world yachts)." [initially a credible argument, but realistically not the same as a paying passenger in the sole charge of a professional skipper.]
He suggests that if a group of diabetics sailed round the world (with no 'non'-diabetics) it would create a compelling case for the MCA to change its rules. [Unfortunately I doubt it helps the argument because multiple diabetics are unlikely to all hypo simultaneously; whereas one on his own at the helm might.]
Probably better ways of lobbying for a case by case assessment, and for emerging technology like CGM to be considered to help prevent untoward events.