Is my 4.5 month old kitten’s breathing normal?

My kitten always breathes like this and pants after 2-3 mins of playing and running. He’s been this way since we got him 2 months ago.

We’ve brought him to the vet, vet initially suspected pneumonia, had him on antibiotics, had x-rays done four times however his condition has not improved. Based on the x-rays his lungs seemed to have gotten worse according to the vet.

His resting breath rate ranges from 70-90 breathes per minute.

We’ve seeked a second opinion with another vet who said he seems fine but I’m just worried cos he breathes like this all the time.