Okay, first I have to say, that I didnt have the time to play Civ 6 lately, so I missed both patches yet. But that change is HUGE! In one game I went with Japan to max out there unique building and getting big amounts of production. Now I will be forced to get as many CH as possible and putting IZ in the best local spot and just so, that it will reach at least another city, not as many as possible anymore. But just cutting the stacking effect of multiple factories/power plants and zoos/stadiums looks like a weak decision to me. It would have been more amazing, if only one bonus would apply, but somehow the adjacent bonus of the IZ with the factory providing additional bonus. Something like one IZ with +3 production, so the factory provides its +3 production and maybe the +3 production of its IZ or just half of it. So it would be at least important to place a (very) good IZ on a spot, but now...
Yeah, but IZ are still important like already said, you still need production, the GE points are still very important and it increases internal trade route outputs by +1 production anyway. Manly it just looks to me, that cities will now be more spread out, because there is no need anymore to get as many city centers in a 6 tile range of some spot as possible. And yeah, times of Torronto being one of the most important City States seems to be gone now ...