That tech world does not make use of the third zone. I just discovered this and also posted about it in the zones thread, So quoting myself here:
>>Just a heads up: If you triple zone a production, you only get the bonus jobs per district only for the first two zones, for the third zone, you only get the extra 3 building slots!
>>This only seems to be relevant for research, as in the end you also unlock the 3 bonus efficiency buildings for each of the 3 sciences. I have found zero usage of this for everything else - so it seems that for any other zone type, you just waste the third zone, by triple zoning it.
So it makes better sense to go for 2 research + 1 CG or Mixed factory, for more job density and avoid some trade (in the future with working logistics) if you don't mind the ineficiency of the factory, missing the designation.
Also, having played to year 2350, and finished all research, you can/will see a difference with orbital rings, as those extra 3 districts will boost any jobs your city zones contained. Not saying that this is better or comparable to an ecumenopolis - I havent built one yet, on purpose, as I'm waiting on the next patch on friday.
Finaly I hate that I can't change or throw a building or two on a colony at will - especially with fortresses, as soldier jobs require the zone. In the past I would throw a fortress on many colonies if I was expecting an invasion, or just as a top up for a bit of naval cap. With the new system this is impossible - you need to rip out 1/3 of jobs from the city of the colony and add in 1/3 jobs for the total of the pops to work as soldiers... which is HUGE, and redefines the economy of the colony/sector/empire.