I got super fat once and lifted a lot of fucking weights just to increase my power and intimidation. I've been in around 20 fights. I've lost about half of them and I've won about half of them, I started winning once I got bigger, agressive, and violent. I think getting bigger helped but it also made me more tired quickly, HOWEVER, it also raised my defense since I also felt the impact of the punch much much weaker. I will provide a few pics of me being a fat fuck back then and me leaning a bit down right now
With that being said, I believe being leaner but still lifting heavy asf is the way to go for winning a fight, what use do I have for power when my dexterity was absolute SHIT. I couldn't Dodge or side step because of my size and I would get winded easily, and when I did land a few punches it wouldn't really help since my opponent could move out of the way or run backwards minimising the blows damage. Technique, agility and endurance play a bigger factor than strength and size, HOWEVER, if you can incorporate strength into all that then you will almost always win the fight.