As someone who has first-hand knowledge of cattle farming in the "Angloamerican West", I can confirm that the OP is correct. A substantial portion of the US beef herd is raised on grass and finished on grain as described. Anyone can see this with their own eyes in many rural areas, internet links from activist groups don't erase that reality.

Raising on grass and finishing on grain is economically optimal in many parts of the US that produce beef. It wouldn't even make sense to factory farm from birth if you cared about profit, since it would be more expensive.

The US is a large place with diverse geography. Few assertions about agriculture generalize.