At which point does a phrase start to become parallel?

At which point does a phrase start to become parallel? For instance, in this correctly written sentence:

Just as many commuters would take the train as would take the bus.

The parallelism begins with the word “would”. But couldn’t it begin in other places such as “take” or “commuters”? Is there a rule?

Just as many commuters would take the train as take the bus.
Or
Just as many commuters would take the train as commuters would take the bus.

Developed for the European Space Agency in the 1990s, the rockets of the Ariane 5 class…

Developed for the european space agency in the 1990s, the rockets of the ariane 5 class *did not yet prove their* reliability as of 2003.

A) did not yet prove their
D) had not yet proved their
E) has not yet proven their

Why is the answer D?

Why is the answer not E? Shouldn’t the answer include “proven”? Shouldn’t the answer say “has” because “as of 2003” indicate present perfect?

Some critics claim that Diego Velazquez, a master of technique and highly individual in style…

Some critics claim that diego velazquez, a master of technique and highly individual in style, had a greater influence on european art *compared to* any other painter.

D) than those of
E) than did

Why is the answer E? Isn’t the question comparing Diego’s INFLUENCE to the INFLUENCE of any other painters? If the answer includes “did”, then isn’t the sentence comparing INFLUENCE to ACTION?

Why is choice D wrong?