Gotta say I like this move better than the Harvey signing. Say what you will about fantasy sites (and they are certainly flawed), but I've always had alot of respect for Matthew Pouliot over at rotoworld. In his September preview for 2019, he listed as the #67 SP, with Matt Harvey #94. The October Fangraphs ranking has Trevor at #80, Harvey not in the top 100.
I guess I can see Cahill as a legit #3 SP, which I CAN'T see Harvey as. I mean, at one time Harvey was a quality pitcher; now, he's just who he is. l think in his case, perception is trailing reality. But in Cahill, you don't have to go back 'before he was injured', you can just look at what he did last year and see he's a solid #3; with a shot at being better, but a better shot of being injured.
Final comment on Harvey; I think 'potential' carries alot of weight with a rookie who is just starting to put it all together; much less impressive when applied to a guy who, in his prime was very good, but now is a bit of a broken down husk.