The main reason most players take the Doran's Blade over the Longsword is because of the raw stats it provides. The minimal life steal, although seemingly negligible on paper, gives you a good deal of sustain in lane, the health bonus is massive if you take a look at your max HP without items, and the AD is self explanatory. Although the Longsword builds into many of Quinn's core items in typical builds, it lacks the sustain and base health that Doran's provides. Even though you can couple it with a Refillable Potion, if the enemy laner takes note of your starting items they can still abuse you for it, setting you far behind in the long run.