Correction: UA, and most other USA based airlines, no longer base earning miles on miles flown. In USA the AS frequent flyer program is not (yet) a revenue based ffp.
Outside of USA most ffp's, but not all, ffp's are distance based. The earning rate can be from 0% to 100% of miles flown, with more for business/first class and status bonus.

Just because an airline has a seat for sale with cash, does not mean its available as a (saver) award. Award flights are never guaranteed. You need to be flexible with date and route.

Most airline ffp's have partner airlines. That is you can earn & burn on other airlines. For example AS is partners with AA, BA, EK & others. DL will cease to be an AS partner soon. https://www.alaskaair.com/content/mi...rline-partners

There is a difference between frequent flying and frequent spending (to get ff miles from credit cards).

It does take a bit of work to understand how ffp's really work and what you can realistically expect to get. Many newbie's have unrealistic expectations. It not as easy as the (for profit) blogs make out.