Ziz is unable to see into the Workshop, but she is perfectly capable of seeing outside of it. Anything created by Jo outside of the workshop (like the omni-tool drones Jo typically flash fabricates) could expose abilities such as his Rome crafting speed, which is something that Ziz can then plan around. Also Ziz is perfectly capable of making her screams mentally inaudible, so for all we know she could already be utilising the full extent of her precognitive powers to assemble enough power to bring Jo to his knees. This is even without noting the relative fragility of Jos defences; if he could be separated from key defences (pin and armour pieces) he is vulnerable. A powerful precog, such as Ziz, would be more than capable of taking advantage of this weakness if given enough information to prepare an appropriate offensive. As such ANY new information of his abilities is dangerous, no matter how inconsequential it might seem to us.
In regards to the potential E88 offensive using subpar tech; I have concerns that this strategy would expose Jo to the precog abilities of Ziz, but let us assume that this isn't the case. I agree with your assessment that Jo can defeat all the E88 in relatively short order using the tech that he has already shown and there is little they could do to stop him. But in this scenario it is unlikely to be just E88, most villain organisations that have territory will likely ally together to take down Jo as he poses a existential threat to them and their organizations, and I am unconvinced that Jo could win this fight using just his old tech. But even assuming he could, the collateral damage in this scenario would be significant and that is enough to bring someone of Jos calibre to the negotiating table.
