I feel ya.... are you sure this Arab mare isn't back-crossed to a Thoroughbred (Race horse)?
In the dog world, people keep telling me they are all individuals, but I quote the old saying in Thoroughbred breeding (the foundation of that breed is, after all, descended from 3 Arabian stallions imported to England): "Blood will tell." I owned an x-race horse gelding much like your mare...a gentleman, but his metabolism just refused to cooperate with weight gain! If anything bothered him, he'd "worry it off." And he found lots of things to get excited about!
After I tried for over a year to "make a pleasure horse out of him," I semi-reluctantly returned him to race training ("because he wants to be a race horse," the knowledgeable horse folk told me, just look at his breeding!") So I did, and danged if he didn't win money! Not enough to pay his expenses, however, but all the while, gotta admit, HE thought he was Living The Life!
Part of it was testosterone, hate to tell ya; I suspect he was gelded a bit late, due to his "illustrious ancestors." A common problem in the breeding business....
And there is the "funny" thing my racehorse trainer told me once, which may offend some - apologies in advance - he said to me "I can always tell a 'woman-broke horse,' because they get coddled from foalhood...(and thus they learn no respect for humans.)
My SAWH said the very same thing about deer in his country, that are raised in captivity for venison...the second generation loses ALL FEAR of man, and THEY are the ones who will hurt a farmer.
So I think your Mini believes, from his life experiences, that he is King Kong...and at that size, it's so cute....until it isn't, right? I'd treat him with all due respect for HIS opinion of himself....and don't get in to a head-to-head with him, if you can avoid it.
How are you, after your illness and accident?