One possibility is that, with the sheer ease and cheapness of hyperdrives, everyone just kinda moved around until population density took a nosedive galaxy-wide.
I agree that for every Ecumenopolis like Coruscant there are probably a thousand worlds with barely a handful of cities' worth of people on them (like Naboo?).
But that doesn't really change anything in the total amount of food/farmland needed to feed everyone since canon(wiki) gave that (very silly) hard number of 100 quadrillion overall population of the (known?) Galaxy in Star Wars:
The galaxy was home to between five and twenty million sentient species, and over one hundred quadrillion sentient beings lived in one billion star systems, interacting with each other through travel, diplomacy, trade, politics, and war.
By any realistic metric a 1500ish Agricops Jedi simply can't amount to more than
a rounding error in the overall food production of the Galaxy.
I can only see three "solutions" for this:
-The Agricops produce highly specific foods (read: luxury foods), that would allow their small number to have a impact on their niche food "market". It feels a bit doubtful considering the Jedis' overall goal and mentality... but to be fair it wouldn't be the first
dirty little secret of theirs we see (and is far from overtaking the whole
baby-snatchers or the slave clone army on the despicable podium...)
-The Galaxy is made of largely self-sufficient worlds (which a low population density would indeed help), so only exceptions like Coruscant would generate significant food trade. The resulting small(ish) overall volume and limited relevant actors in said trade would allow the small number of Jedi to have a notable impact. But even that is doubtful since aero/hydroponics isn't exactly rocket science, so things like a lack of "farmland" shouldn't really be an issue anyway...
-The Agricorps specialize in timely high value food stock (read: humanitarian help and similar issues) which is a really cool idea, but I'm having hard time meshing that idea with the whole Clone Wars thing...
(I would have added a fourth option where these jedi work to make new better foods and hence contribute to the overall food production... but Star Wars doesn't ever see
improvements so that's not really possible)