this is something in clinical research called the dichotomy between pragmatic and explanatory trials. RCTs like this aren't useless even though they don't specifically answer the question YOU expect to have answered, which is essentially: "controlling caloric intake, what impact does restricted meal windows have on weight gain/loss/other measured outcomes?" This is an explanatory question--it seeks to isolate a variable (meal timing) and explain it's impact on people.

in contrast, the question the RCT is REALLY asking is essentially: "comparing ad libitum intermittent fasting (which is a very easy thing to suggest in a busy clinic) to a very expectably superior intervention like calorie tracking and restriction, does IF end up having some efficacy?"

it's a different question--more realistic of an intervention to provide and monitor (because you don't monitor it at all really...)--and so ends up being perfectly valuable if you interpret it for what it is, assuming the rest of your critical appraisal of the paper passes muster.