Clearly. But, if I may say so, the question that sparked this was "is it better to work two plains tiles or appoint a specialist"; you've slipped around that question by advocating a third approach (which I'm not complaining about - if the third option's best, why not?)
Hmm. I'm sure somebody already did Math on it, but shouln't be too difficult:
A Specialist is 2 plains Cottages. The Specialist giving 3

, the plains-Cottages giving 4

and 2

, that's a lot more. Actually I'm a little bit surprised that it's that much, but I may be underestimating the value of

. Thing is: 1 Specialist, or lets say 2 create lousy 6

, on Marathon I need 300 for the 1st GP, 600 for the 2nd, 900 for the 3rd, getting 900

already takes 150 turns, that's too long, games are
decided before that imo, and units like the OP-phant live forever and kill anything up till Rifling, for what do I need tech?
No idea, but I find outproducing the AI a lot easier than outteching, besides, Trebs / Cannons + any STR8 units win everything, I mean really
everything.
Btw., I do not even work Specialists outside the GA-Chain (except scientists if I plan to run Buro and need an Academy) , I even find non-riverside grassland tiles worth working, all those could be units conquering huge AI cities that have nicely grown Cottages because AI whips to little.