Especially if they're 6'3 and have been cutting muscle to make 175, sure. Moving up in weight could be beneficial.
There are a lot of misconceptions about putting on muscle (and he only put on 10 pounds or so). He mainly bulked up by ramping up his caloric intake and cutting back on pointless long-distance cardio. He did plenty of stretching and high-intensity cardio to maintain his speed and agility.
Michael Spinks was 6-2 3/4, 76" reach classic boxer/puncher type. Marciano was 5-11, 67" reach aggressive brawler type. If you can't see how the difference in style and physical attributes would be affected by such weight gain, I really can't help you.
I've never said that Rocky couldn't do it but it's much, much easier to bulk up effectively when you're significantly taller and have broader shoulders and longer limbs.
I think he should have bulked up. It was more a musing about how Rocky must stay at 189 but Spinks can add 25 pounds.
Again, Spinks was much larger framed and longer... and fought in a completely different style... Both the physical and stylistic attributes make much more sense for a Spinks or Jones than than for a Marciano...
He was an attrition guy whose style was based on flexibility and stamina. I do not see that an extra 15 pounds helping either. Again, if Goldman thought 200 was his best weight, he would have arrived at the ring at that weight. As it was, he arrived in the same range whether his opponent was 180 pounds or 210 pounds. This conjuring up of an improved version of Marciano by neophytes is somewhat of an insult to the great work of Charlie Goldman.
Read the link I sent you. Spinks didn't add 25 pounds. He just didn't come down as much. His natural walking around weight was between 187-192 pounds. Rocky's physique was a lot different to Spinks'. I'm not sure what Rocky's walking around weight was, but maybe if he'd have bulked up to 200 pounds, it may have affected his speed and his stamina. Rocky's stamina was one of his best attributes.