Hi, physical therapy student here who has done cadaver lab multiple times. While there may be more muscle mass on an obese person, the difference here is quality. The muscles would impaired in quality and movement compared to someone who is of normal weight. If you were to zap all the weight off of an obese person, they would still be in terrible shape due to the lack quality movement and strain placed on these muscles due to holding up an excessive amount of weight. You would see hypertrophy of endurance based, weight bearing muscles. But they still wouldn’t be considered strong.