It would be nice to have the option to accept and finish quest with one click or button.
Right clicking takes 3 clicks to accept a quest and finishing takes 2 clicks.

You can use the Blizzard quest window to accomplish this. There is a setting to toggle whether it is hidden or not.

I will add to the previous comment that the goal for Storyline is to offer a better experience to read the quest text, not to skip it. Adding such feature goes against the goal of the addon.