I'm not really a fan of trading Soler AND Montero for Smyly. Smyly has two years control left, is an extreme flyball pitcher, and does not have the profile to be an effective reliever. If the Cubs are trading Soler, I want someone who has a higher ceiling and/or has more control than two years. I mean your best case scenario is you're paying him in two years.
Smyly has already shown he's a decent reliever though. In 2013 that's literally all he did for detroit and at 24 had a 2.37/2.31 ERA/FIP. As for being a fly ball pitcher it's mainly just his fastball. His slider on his career has a 44.1% GB rate. His Cutter has a 49.4% GB rate. His change up has a 45.9% GB rate. Those are all above league average. He didn't throw his 2 seam fastball in 2016 but on his career that has a 29.1% GB rate and his 4 seam fastball is at 29.2%.
While I certainly would love a lengthy controlled arm with less warts than Smyly I'm just not sure that's out there for Soler. His bat is obviously super promising but you're having to get buy in on his defense being at least half way acceptable in LF. My take is that Smyly has the tools to be a top of the rotation starter he just needs some work on his fastball. His fastball is left up in the zone too much. His zMov on his 4 seam is 11.6 and his 2 seam is 11.7. For what it's worth, Arrieta had similar issues on his 4 seam before coming to the cubs. in 2013 his 4 seam had a zMov of 10.6 and even his sinker was high at 11.4. And unsurprisingly, his sinker had a 40.9% ground ball rate and his 4 seam had a 38.8%. So, that strikes me as something fixable.
Realistically speaking who would Soler net who's better? For example, I don't think Soler and Montero even get the conversation started on Archer. It might on Odorizzi but is he really a better option? His ground ball rate is 34.5% to Smyly's career 36.3%. His career k/9 is 8.26 to Smyly's 8.71. His career bb/9 is 2.74 to 2.54 for Smyly. His career soft contact rate is 17.9% compared to 20.7% for Smyly. He certainly had a better 2016 than Smyly but I don't think he has as much upside. As for other teams, I doubt the sox really want to deal with the cubs but there's no way Soler gets the conversation started on Sale. Reports I've read suggest the sox don't really want to deal Quintana. Rodon is interesting if available but I doubt Soler is enough for him either. I'm personally not high on Sonny Gray. Think you can make he case for Gray maybe being obtainable with Soler but I'd rather have Smyly personally. Like wise, there is Shelby Miller but I was never that high on him either.
I think of the available starters he has one of the highest ceilings because there aren't many pitchers who have 9+ k/9 potential with a sub 2.5 bb/9. Last season there were 10 starters who had 9+ k/9 and a walk rate under 2.75. They were Jose Fernandez, Max Scherzer, Noah Syndergaard, Michael Pineda, Justin Verlander, Madison Bumgarner, Corey Kluber, Danny Duffy, Chris Sale and Kenta Maeda. Sure Smyly has issues but if he didn't he wouldn't be available because of those players listed, Pineda is probably the only one truly available. Duffy *might* be but that's only because KC might not be able to afford him. And in either case, Duffy and Pineda are 2018 FAs. If you're telling me they can get Smyly for less then by all means but I think that's the realistic price it would cost.
Edit: Verlander is also probably available. When I was writing this I was more thinking about as a building block piece so he slipped my mind. Basic gist was that arms of that caliber are rarely available.