I think that the farm is meant to be lategame content in the grander scheme of things (and I think it should be more profitable to compensate the price), I think further down the line the idea will be to be constantly travelling between the 4 islands doing small quests in all of them, rather than trying to finish all the content in one before moving to the next, also I think the trainers are there mainly to fix big stat deficits you can have in some runs where you mess up, so I don't think the intent is to use them to minmax by trying to bring everything to 20 before doing any other quests. You can do it, I just don't think it will really unlock anything cool and is more of a trick that requires grinding.
Since the game still has a lot of content to add, I don't think the balance is a priority, which is why you can use cheats in the menu, to access and test the content that would otherwise only be meant to be accessed late into a playthrough. If for whatever you reason you don't want to cheat, even while being aware the game isn't properly balanced and probably won't be until a lot more content is added, I think one of the casino games was poorly designed, the one where 2 dies are cast and you need to bet on either highs or lows, I remember 7 counting as a "high" so betting on high actually had a positive ratio in terms of risk-reward, so gambling non-stop would generally be profitable, savescumming every once in a while to get rid of any unlucky bad streaks would make it even more so, so it was decently fast and reliable, way better than working for the money given the current work options.