I'm no expert and have no medical qualifications.
But I would observe that strokes are of very variable severity, and that people can make good recoveries even from some of the more serious ones. A presenter of Current Affairs on the BBC, Andrew Marr, is one such example, having suffered a fairly major stroke a year or so ago, and now back interviewing and fronting programmes on British TV, without any apparent ill-effects.
I'd say that something like ALS (Motor Neurone Disease) or a Glioma brain tumour would be better candidates for "the most debilitating disease one can get", as they are effectively a death sentence and involve an inexorably debilitating experience in the process.
Nonetheless, the "living death" situation which can result from a stroke, sometimes with little or no prospect of improvement, should be pretty high on anyone's list of things to dread, as you rightly imply. The loss of control over one's day to day life, not to mention the loss of dignity, must be at least as bad as any amount of physical pain that one might experience in other illnesses, in its own way.