I’m obviously far from expert on this, but this is why I believe weight training is SO, SO, SO much more important than cardio for overall health and weight loss. Putting on a bunch of muscle does a couple of things. First, it gives you more lean mass which needs more calories to survive and can increase your metabolic rate all day long. That’s one of those no-brainer benefits - it even helps when you’re sleeping. Big dividends. But also as we age it becomes harder and harder to stay strong, even for the basic functional strength needed to perform regular daily tasks around the house. This dawned on me two years ago and I wish I had come to the realization a few years prior, but it is what it is. I will continue to lift through my 40s, and hopefully beyond, because it will only get harder to put on muscle with each passing day.
That said, to your point, I agree it’s 80% diet. Which is why I still walk around with 20lbs of extra fat I’d rather not have. It’s a nut I still need to crack, but I’m working at it. Eventually I’ll get there.