Small custom shops used those. I had a Stanley router just like the one in the picture.
Years after those were no longer available I had to make a few doors with the curves routed into the corners. No fun without the jig .
do those culottes have daisies on them coop? seriously i do them on the router table because i don't have a morticing machine and I'm too lazy to set up a fence on my plunge router, maybe if i make an adjustable fence for the plunge router i would use it more.
There are times when I need to do a stopped plunge on a router table, but I really dislike doing it. I'll look for any other way to cut them first.
I'd take a look at making a mortising jig that you could use on lots of other projects that would use a plunge router from above. It's much safer and I think you'd be happier with the more consistent results.
Here's one that doesn't require using guide bushings -
I also like Philip Morley's jig that uses guide bushings -