Design flaw?
The FAA has stated, in the language of the AD, that the autothrottle must not be engaged, or re-engaged, after the thrust levers are advanced to the takeoff setting, until at least 400' AGL. Not really that complicated.
Imagine actually having to do pilot **** in an airplane. Imagine actually having to fly the damn airplane. God god, what were they thinking?
If the autothrottle isn't engaged for takeoff, or disengages, it is NOT the end of the world. Two pilots. One flying. Another who really can ensure that takeoff thrust is set. If the autothrottle isn't engaged or disengages, focusing on re-engaging it during the takeoff roll is idiotic. Fly the god damn airplane.
This shouldn't be an issue, but not because the buttons are too close together, or because there is a perceived design flaw. It shouldn't be an issue because the operator needs to hire pilots, rather than mere button-pushers who can't continue the takeoff with manual throttle manipulation. Are we really so short of competent aviators that there are those who can't continue or conduct a takeoff without stabbing the automation during the takeoff roll? This isn't an airplane design flaw: it's a pilot flaw.