I don't think that's right. Sorry, but Penny was good toward the back half of the year, and KJ got hurt. Sure KJ produced well comparatively, but no way I'd trade Penny and an early first for KJ. Penny is still a first round RB, and by all accounts is looking very good this year, too. His value should not have decreased that much in my eyes. If it has, you're much better off with Penny and an early first than KJ. Projecting forward, not looking back, that's just not a good offer for anyone to make. Penny was an early first round rookie pick last year, and he did enough to not have his value torpedoed to the extent where he's a throw in to get KJ.
@OP. KJ is worth more than Penny, so you'd want to get Penny plus, for sure. If you can get any first on top I'd gladly do it, personally.