All carbs become glucose and provide the body with 4 calories per gram. Yes, there are varying efficiencies, and yes, absorption does matter to a certain degree (GI/GL also matter). However, for the sake of this discussion, people get fat and suffer from diseases like metabolic syndrome, diabetes, etc. mostly because they're fat. The reason they're fat is because they eat more energy than they burn. It has very little to do with what they eat, and everything to do with how much they eat. It has been this way since forever.
You’re incredibly smug for being so wrong. Concentrated simple carbs invite an outsized insulin response, among other dynamics that do put the body into fat storing, as opposed to fat burning, mode.
People who are fat have overeaten relative to what their body requires, but they’ve also likely eaten poorly, which, such as with the exaggerated insulin response, has led to more hunger and a negative cycle.
As any number of people here are trying to tell you either from their direct experience or from links with scientific studies, this is the case. That is why formerly fat people can often eat more, though of different stuff, than they were able to eat when they were fat.
Also, the fat for many diseased is, like their disease itself a product of what and how they’ve been eating—rather than necessarily the primary direct cause of their illness.