tbh it's "easy" if you're also doing a pretty specific focused diet. (maybe simple would be a better phrase - it can be reduced to very simple steps. mentally choosing to do this and enduring it is difficult, but the process itself is straightforward.)

like the worry about sauces is true but if you eat mostly chicken and rice and one slice of bread a day you can really get that variability down. when I was heavily restricting I would only cook very simple things like that and otherwise eat packaged food, and it certainly worked to lose weight. but you sacrifice variety and flavor and you'll feel kinda stressed and hungry for months at a time.

the last factor is living with people who are not dieting - I personally think this makes the required willpower basically impossible. if there is food in the house you will eventually succumb to the temptation of eating it in my experience. it's much easier if you live alone and only have the diet food in the house at all, buying nothing else, etc.