Don't make it 1 turn, make multiple items completable in a single turn, so big cities with attached resources/spells etc. can compete with many smaller cities.
Agreed with the sentiment, your phrasing was off.
Don't JUST lower the 3 turn limit to 1 turn limit. Allow as many items to finish in a turn as you have production for.
If I make 50 hammers in a city and I queued 3 items costing 20 hammers each then it should finish 2 and a half of them... Anything else is stupid, unfun, and pointless.
Also, what he heck is the point of investing into a city on the production side with such an arbitrary limit?