I've lived my entire life between 600 and 1200 feet AMSL, venturing to the higher elevations (9,000+) of Utah, Colorado, Montana, Idaho, and Wyoming several times.
If I traveled by car, i have only mild areobic fatigue on moderate hikes up to 10,000 feet. I'm slow, my quads burn, i sound like a steam locomotive, but I push my fatass through.
If I traveled by air, even several days after arrival in SLC or Bozeman, I've got headache, nosebleeds - and most recently, dizzy spells - at 9000, even with rigorous hydration and little exertion.
In 1986, as a 30 mile a week runner, flying into Pitkin County in 1986 kicked my butt. I couldn't ski for 2 days.
In 2018, flying into Phoenix, (1135) then driving to Boulder Utah over several days, I hiked 3 miles to 10,000 and fished for 2 hours with no more than the expected huffing and puffing.