In some cases you are correct, the plunge router works great. I have two plunge routers a smaller one and the Dewalt 621. Neither would have been a match for the repairs I did.
In some cases, I just chopped the mortises. In some locations, I drilled adjacent holes and finished with chisels. I also used a self centering dowel jig to drill holes and finished with chisels.
I warm up to do the hand work by chopping practice mortises.