the other answers here are more detailed, I just wanted to state it simply.
Again, the digestion point seems to reinforce CICO. If you gain weight because your digestion is slower (let’s grant the point), it’s not because your body some how treats calories differently, it’s that you’re getting more calories from your food. Your calories in are higher.
Not to mention that diet products have existed to game your digestive system to absorb less calories from your food. With the rationale being… less CI in CICO. See also: folks abusing laxatives for this purpose
Throwing information out like this (w/o source and at best poorly replicated), that CICO is useless because of digestion rate, is incredibly dangerous because it falsely legitimizes that hopelessness. It traps people. And it maybe only applies in <1% of cases, where you have not just obesity but also compounding, very specific digestive issues. The opposite is also true — you don’t just drink coffee to knock off enough cal absorption to make a diff — you take laxatives you don’t need and have extremely abnormal, frequent BMs.
Anyone and everyone can lose the weight. It’s just CICO. You gotta figure out your input and output to account for the minor individual variances, and lock in a lifestyle to do it. But it’s just CICO at the end of the day.