3. Snell is rarely a workhorse
The main drawback here is the fact that Snell doesn't pitch a ton of innings. Aside from his two Cy Young years where he reached 180 innings both times, Snell has failed to surpass 130 innings in his other six seasons (admittedly one of them was the COVID year). This fact alone is enough to convince me that Snell is not the type of pitcher the Cubs should be signing right now.
Last year, the Cubs used their bullpen a lot and for half the season, they were unsure who their reliable arms were. When they found the three guys to hold it down - Mark Leiter Jr., Julian Merryweather, and Adbert Alzolay - they leaned on them in every close ball game and there was a heck of a lot of those. Heavy bullpen usage coupled with the departure of Marcus Stroman earlier this month means the Cubs need to sign someone who can eat innings and be a rock in the rotation.
Right now Snell would be the flashy signing, but the smart starting pitchers to bring in would be someone like Arron Nola or Jordan Montgomery. Either of those two would be similar to the Jon Lester signing, and give you a reliable five innings or more every fifth day.