Scaling shouldn't be the one factor in your choice. It should be the last thing you consider.
Not to make any assumptions, but if you picked an uncommon subject like food tech, you probably enjoy it. If you enjoy a subject you'll be motivated to study, and even go beyond the syllabus which will be more beneficial to you in the HSC than doing a subject just because it scales better.
Regarding the economics and food tech HSCs, the economics one would be more difficult and would require a lot more study. Just my opinion but the food tech HSC exam looks super fun lol. If you're doing other heavy subjects then food tech would give you a nice break.
But if you really love economics, then you can stick with that also. Remember that you have all of year 12 to make up your mind so don't rush into things.