You're right. There's so much more to it. You have to ask Why you eat. Is it for self-comfort, for sustenance, out of compunction? It's What you eat. If you're on a vegetarian diet but still eat a lot of bread, your exercise won't help. If you're on Paleo but not lean, good luck.
And you're right about the balance. It takes time for the grehlin and leptin to balance out again, the gut biome to repair, the salt and sugar cravings to die down.
And then there are the personal issues to work through where therapy may be helpful to overcome stressors and trauma and disorders.
All that before you even step foot in the gym!
Yes, eat less move more is as basic as it gets, but there's more to it than that.