Lived here for 8 years.
I do not agree.
Boulder is extremely OVERRATED for training. For altitude it's far too low. The weather is atrocious 100+ inches of snow a year, has some of the worst air quality in the country. The dirt roads are gross. Cost of living is just stupid. If I'm paying this much I'd rather live in California.
It snows in JUNE here. 8 months of measurable snow fall... Let that sink in. GROSS.
It is one of the windiest places in the United States. Wind Storms are a real thing here.
If you want Altitude there are significantly better locations.
Flagstaff - real altitude
Albuquerque. Access to 4800ft to -6500ft. (easily live at 6200ft above tramway) Training locations are unrivaled, some of the best trails anywhere. FLAT uninterrupted bike path at 4900ft 18 miles long point to point. Some of the best weather in the US. Less windy than Boulder. 10 inches snow a year.
Mammoth. Real real altitude. Winter season is WAY shorter than Colorado.... You don't get nasty spring snow.
Big Bear, real altitude, one of the Southernmost altitude location .... SUPER short winter, and if it's bad a quick drive down to the valley / sea level where it's always nice.