You always look for any instance to downplay Kizaru so I'm not expecting any objectivety from you but I'm still going to try
A sigh bubble once isn't the same as gasping for air like Ray was near the end of the battle. If Oda wanted to portray that both were getting tired, both would be huffing instead of just Ray. On top of that, Rayleigh was literally complaining about his old age in that same panel, this was done on purpose.
and was the only one injured
Because he literally ignored Rayleigh lmao
There's a reason why Rayleigh managing to stop Kizaru was portrayed as being a an impressive feat for Rayleigh in-story with while for Kizaru getting stalled was basically embarrassing. A character getting hyped for punching above their weight like Ray was doing in that instance.
Prime Ray is another story, but Old Ray doesn't push Kizaru past high diff, he'll collapse before that.