No, he didn't hurt them.
Why? Meat project. You'd be surprised what a tall and seemingly skinny bird x a normal bird would make. They actually produce something that looks a lot like a Cornish. Since the tall Oriental Gamefowl have so much muscle tone and a long body to lengthen it out, plus Marans are decently heavy, have moderately good growth speed, and a nice, level set body - The two combined will widen the body, shorten but enlarge the chest muscles, and all together make a good, compact, meaty bird.
Here's a similar cross of Thailand Gamefowl x hatchery Rhode Island Red. Now, Thais are lesser in size and meat than Shamos, and Production Reds much lesser in meat and size than Marans. . . So take this beefcake hen and make her a little chunkier.
I meant to say "seemingly" skinny about Shamos because they actually have a lot more muscle than most other breeds, they only seem skinny because of their hard feathering and tall bodies. (hard feathering is how the feathers press firmly against the body, showing off the true shape of the bird and minimizing the fluff which makes it appear bigger)
Pink - Well said. Shamos are VERY sweet, kind birds, just not to other roosters.