I have literally previously outlined how to customize the corruption list so you can get 10 affixes that do not hinder your build. Works for any build you prefer to use. I do Plague 4 Pestilence runs with 10 mods all the time. And I do not use those unique rings. I didn’t when they were broken/OP, and I don’t now.
Taking an affix that deletes your focus as a mage on purpose, is like taking one that removes all your stamina as a melee character. You have a choice. If you choose to make it difficult for yourself by deliberately taking the corruption that makes playing your mage nigh impossible, that is another matter altogether. But still, a choice.
If like the other user, you also did not know how to do this. The issue there is on your knowledge or expertise, not on the mechanics of mage play or the Pestilence mode.