You just didn't cook it long enough.
Like the song says,
Pease porridge hot and pease porridge cold; Pease porridge in the pot nine days old.
Cook up that mutton at the slow boil for three or four days, chucking in handsful of strong herbs and garden veg every other day or so and letting it get tender, and then start washing it down with tankards of good porter or bitter and wiping the plate with good hot, fresh bread anointed with freshly-handmade butter and currant jam, and see if you don't change your mind.
A bit trickier sans crock-pot. Who'd keep the stove going at night?
Kind Sir, I truly believe that the Tankards need to commence
in anticipation of the mutton.