It's a Baldwin AS416. Not too many Baldwins around to see. Long ago when my wife was first learning about the various manufacturers, I said, "You'll probably never see a Baldwin" and yet within the year during a visit to the Tennessee Valley Railroad Museum in 1990, what should appear, but an operating Baldwin VO-1000 fresh from the paint shop! It's since been removed from service because of main generator trouble.
Just what happened to switchers nationally? I'm guessing that rebuilt geeps now fill the role? I can't remember the last time I saw a switcher in service, outside of those owned by industries.
There are fewer yards. If you abandon a branch, does the junction where it tied into the main still need a yard? Bigger yards. Abandon the intermediate yards, and those that are left have more to do, and are liable to do it to longer strings of cars. As far as spotting cars on a particular track one or two at a time, humps, trainmasters in the tower, and gravity do most of that now. It doesn't take a special small locomotive to shove them all up a hill high enough to enable them to wander down to where they belong on their own. And, yes, road locomotives that are lighter and able to handle tighter curves than the typical Yellowstone type articulated.