WTO

Yes, I think the past tense should be Ok here.

But in GMAT philosophy, you are required to choose the best answer, not the perfect one. So don't expect ETS to test you with a question in a 严谨 way you prefer.

WTO

过去时表示过去某个时点的动作，不具有延续性，跟后面的anually搭配不恰当。而后面的earned是和then以及as。。。搭配的，说明是“作为director那个时候，那个时点”所赚钱的水平，因此用过去时。