Firstly, magic, and especially mass spells (both light and dark), are very helpful in this situation. I always use them.
Secondly, a 20th-level Warlock with expert education and in a real game with artifacts rarely has an attack power of less than 20.
Thirdly, if an Academy mage of level 15-20 starts creating mini-artifacts, they will be left without upgrades and the Mage Guild, as there are still few resources during this period of development.
Of course, mini-artifacts and the partial ability to block enemy magic are a strong blow to any opponent, but in principle, it is not fatal for a Warlock. Also, don't forget about the chain of elements.