A question about omission

Solution 1:

Much depends on the meaning of so. I believe that is it used by Moore in this way:

Cambridge

so:

used usually before the verbs "have", "be", or "do", and other auxiliary verbs to express the meaning "in the same way" or "in a similar way":

Moore is saying and in the same way that an egg should be seen as a simple shape, the other listed things should be seen as simple shapes (and not as their functions might suggest to us).

The parallelism implied by "in the same way" is between our perception of eggs and our perception of all the other things. From that viewpoint, your introduction of being is unnecessary.