Some of the standard needles brands adapted their new generation models to fit cartridges better, that's why for example dragonflies on their new generation have motors with more torque so, they run them nicely but the real problem that i see is that, even if you buy them (standard/carts) thinking on using both methods, changing the machine to move it from standards to carts is time consuming and you end using them just for one of the choices, so it's not so "on the fly" like companies want to show...
By the way, not all carts only machines are stroke/give adjustable, same as regular needle brands, so that's not an advantage of ones to anothers.
For lining with rotaries imo you have to adapt your hand to them but maybe they need the "slap" motion of a coil, which I think that some of them (cutback whip /sidewinder) have it on his movement conception... But yeah they line different, so I don't think it's a problem of your stingray/carts combination, they're nice machines.