Rivas is just 23 years old and won't eat up a roster spot, but he also carries minimal upside, per Sahadev Sharma:
Kemp provides Oakland with depth at second base in the wake of trading Jurickson Profar earlier this winter. He can also profile as a corner outfielder, which adds versatility that Oakland no doubt covets as they look to return to the playoffs once again in 2020.
For the Cubs, moving Kemp (who was out of options) creates a bit of flexibility on the 26-man roster, while also supposing the front office might indeed be inclined to give Nico Hoerner the inside-track to the everyday gig at the keystone. With David Bote, Ian Happ, Daniel Descalso and Hernan Perez all capable of playing in the four-hole as well, the Cubs have a variety of options that'll compete for playing time during the spring.
Should the Cubs decide to give Hoerner some seasoning at AAA in favor of a rotating cast of veterans at second, Kemp's presence remained mitigated given the plethora of options. What Kemp doesn't do is shed salary, as his pre-arbitration salary for 2020 is expected to be near league minimum.
Kemp hit just .183/.258/.305 with an ugly wRC+ of 45 in 93 plate appearances for the Cubs last season.