Baumann is a huge risk, more than Wells. His stock has shot up after his time in Bowie last year. I am a big dynasty player, and Prospects Live has him as their 264th overall player, and Wells isn't listed. Prospects1500 has Baumann as our 10th prospect, and Wells as our 17th. MLB Pipeline has Baumann 10th and Wells 20th. He has a lot more upside than Wells IMO.
Pop has the TJS recovery but a two-pitch reliever who was a lock-down guy in AA is a worthwhile risk for the Rule 5 draft, especially with 26 man rosters now. If I were a GM, I'd rather take the chance on a guy like Pop who could be a very good high-leverage reliever over a guy who might be a back-end starter/long reliever.
Well, you listed six, I listed six, so that could work.
I’m not sure Pop is a risk to get picked, given that he had TJ and didn’t really have any post-recovery time to do game work. I would certainly choose Wells if I were the Pirates or the Rangers, because they both need pitching really badly. Not sure how risky the others would be. That’s worthy of a separate post.
Guys who could be exposed to the Rule 5 draft if not added to the 40 man roster: Baumann, Lowther, Wells, Mattson, Hanifee, Pop. (There’s a few others who have no risk of being picked.). How many of those get added determines how many need to be removed (more or less; right now we have 20 pitchers on the 40 man and I’d expect it to stay at about that number).
Ace is like top 5 to me. You pretty much expect to win every night no matter who you are facing. Bieber, Cole, Verlander, Degrom, Scherzer. Outside of those guys I can't think of any I would call Ace nowadays. Top 20 would be so called Number 1's but not every Number 1 is an Ace, IMO.