It would be similar in usage at that point, but dissimilar in quality. Disregarding the cranequin for a goatsfoot (as the cranequin would be for REALLY high draw-weight crossbows that would be overkill here, though if you want we can discuss having 8x the power), you're still looking at an increased fire rate, triple the power (lockbows being around 50 lbs draw weight, while early stirrup crossbows being 100-150lbs, and composite crossbows with loading devices generally being 450lbs+), and significantly more penetration joule-for-joule. A goatsfoot can load in more positions (kneeling, bending, standing) compared to a stirrup (bending only), and reduces fatigue compared to spanning by hand. Power in a crossbow also affects its range and its trajectory, don't forget. Metal quarrels had both increased weight (improving trajectory and energy imparted) and specially designed heads, relying more on force rather than sharpness to 'punch' through armor and skin and bone, playing more to the strengths of the crossbow (which are surprisingly different from a longbow ballistically - is ballistics the right word for non-bullets objects? Whatever, you know what I mean).

The stirrup was a major advancement, increasing firing rate, position, and power, but not nearly to the degree that anyone would mistake it for roughly equivalent to a composite crossbow of the type you laid out. It would be LESS of a massacre, but it would still need to be lopsided in some way for the outcome to be in doubt. I guess you might say that at that point it's more like a Mosin-Nagant vs. an AKM, though that still misses the penetration/damage/range factor. IE that a Mosin-Nagant can penetrate as well as or better than an AKM, while a stirrup crossbow with wooden limbs spanned by hand would struggle to penetrate padded armor, whereas a composite-limbed bow with a loading device and metal quarrels could realistically penetrate mail and even lighter plate armor - and of course, all of that applies to the increased force imparted to skin-and-bones to unarmored targets, though not as important.