Well I think of myself as a DJ and I totally agree with you. The real magic happens in the production part. If you just take samples from another source and put them in, you are DJing with samples… sometimes to an extend where the samples take over and I do not actually like that.
I am however also producing, but mainly songs for artist friends of mine (and sadly none went to the charts yet hehe.) and I think if you are a good producer you can become a controllerist. Like moldover I also play guitar and sing, but I would not play my guitar on a controller…
You can check out this song I put together, it is 100% sample loops, some I took and some from Logic sample packs…
http://soundcloud.com/terry_42/honkytonksitar
I am sure I could take all that samples I used, arrange them on a button box and improvise the song more, but I do not think it would sound as good…