You don't even have to eat "right", just eating less would be enough. For example I still love my pizzas and hamburgers, but I eat smaller portions so the amount of kcals I consume is in line with what I need.
[edit]:
> but increasing usage of calories isn't as 'hard' as going to the gym all the time (e.g. walk to work, take stairs, etc)
Not all the time, but given some baseline of activity predicated on having a normal routine that's fairly good (ie including routine exercise like your listed examples), increasing activity further is likely to be more strenuous than lowering consumption. Or in other words, once you're past the quick wins that you can easily integrate into your day you're more likely to get results from decreasing/improving consumption.
The most important thing is for people to fix the kind of food they consume so their appetite (hormones) self-regulates. Were people thin in the 1960's because they were counting calories?
https://www.healthline.com/nutrition/debunking-the-calorie-m...
> Saying that weight gain is caused by excess calories is true, but meaningless. It tells you nothing about the actual cause.
Most likely people were thin in the 60s because they consumed less calories then we do now.