I can only respond on what I see- first, yes I agree that food seems to be the major limiting resource on army building.
I'm not going to give actual numbers, but here goes:
I have the same number of workers assigned as farmers as I have assigned as lumberjacks. I have 25% more gold miners than farmers or lumberjacks.
I have the same number of gold mines as I have farms. I have half that number of lumber camps.
All technologies are researched (and have been for quite some time).
As far as hourly income goes, mine has been increasing steadily compared week to week.
As of today:
The resource I gather the least of is wood. (expected, as I have fewest lumber camps versus other buildings)
Food gathering is 6.5% more than wood. (yes, that's six and one-half percent)
Gold income is approximately 47.5% higher than my wood generated.
Yes, I actually check out what my hourly income is at least once per week.
No, I haven't seen a decline in the amount of food generated- but I do agree that it is what limits my army-building the most.
It's been said before, but buildings (mines, farms, lumber camps) have a bigger impact on resources gathered than workers do.