We never said they are not essential.
we just said that for now, shortages will not lead to production drop.
but this was a long time ago and the number of factories producing the upgrades is much higher so within some weeks, we will announce a normalization of the factory maintenance units and shortages will lead to production stop.
The numbers you need are now smaller and the numbers produced by each corporation are slightly higher.
the corporations producing them are, and will remain very profitable so we expect the number of corporations to continue to grow.