I agree, the guy who played him did seem to be a decent actor, and I always wonder why they didn't use the character in a larger role, especially since they had no other men on the show in that age range (they wouldn't until Dave Phillips later in 1982).
Did all of your family unit leave the show at the same time? I read there was talk of a spinoff for the Cummings family but that didn't happen.
When you watch the episodes of that time, some of the new actors brought in are kind of poor - just comparing Susan Scannell's very nuanced and vibrant work or the solid work from the guy who plays Russ, and then some of the other younger leads who were brought in, many of them were very wooden and it took a long time for them to improve, if they did. I think that's why your work stood out for me, as it was a little green, but had real talent and potential.
There was a very nice scene where Jill talked to Peter about her father and her lonely life - it was a poignant little moment, done just right. I also liked the scene where Jill was bluffing to Peter about the SATs. I think Jill brought something very different to the show.