I'd be surprised if elite level pro and amateur cyclists breathed in any unusual way unless they were at lactate threshold. I've seen pros chatting almost normally while riding at a pace that would leave me gasping for air and passing out within 5 minutes. And recently Mark Cavendish had a few choice rants for the TV motorcycle crews who were -- possibly deliberately -- influencing or rigging a race to provide a draft for favored riders. Cav was riding very fast to catch up yet still was able to loudly repeat the same complaints to any passing judge or cameraman passing on motorcycles and cars. He wasn't wrong. I was mostly impressed that he could speak loudly and fairly normally while riding so hard. I'd be on the verge of passing out from exertion.
From the perspective of the 50+ forum, I could come up with all kinds of reasons and excuses why I'm getting slower despite working harder to stay fit. But it all boils down to "I'm old, and getting older."
Yeah, I could wish for all kinds of things to delay the inevitable. I had hoped my window of opportunity to continue getting stronger and faster would remain open at least a crack until I reached 65. But, nope. I'm about to turn 64 and I've weakened and slowed dramatically this year after a few consecutive years of steady improvement after resuming cycling at age 57. In 2015 I was starting from nothing, extremely poor fitness, so I knew I could only improve for awhile. And I did... until this year. That window of opportunity closed last year and it won't get any better without PEDs.
That's just the reality of aging. It varies for different people and some folks may continue to improve or at least maintain measurable fitness awhile longer.