I have been farming AI 5s for a while and have only won 2 upgraded cards.
It is very true they are easy, and if they had 100 health, they would be much worse then AI3s.
They seem to use random combinations of decks, some which do not seem to work well together, and when they do have a combination of elements which can make a decent deck, they are stuck with what seems to be premade half decks joined together.
For example water/death can make a poison rush deck. But it still has useless cards like mind flayer, without aether quanta, and vultures, which do not belong. Of course, if AI 5 suddenly had super organised decks with strategies, they might as well be called 'Slightly more False Gods', and people stuck between AI 3 and False Gods would be stuck.
I think the solution is to cut down on the number of Half Blood decks, to around 12 better built duo decks (hopefully with each element used twice) and 12 mono decks. Then they would be more of a challenge to everybody, but still not become as powerful as the False Gods.
That was just my opinion on this matter though.