LOOGYs are my single biggest axe to grind about roster construction. You only have 25 roster spots. There are not 30 lefthanded pitchers out there who are good enough to justify a roster spot for getting 1 or 2 outs 3 times a week and who are not good enough to justify a roster spot for other reasons. There might not be 5. Blevins and Perez are not among that 5, Perez's freakish season last year notwithstanding.
If a guy is not good enough to be on a roster for another reason (for example, as a standard middle reliever) and can't reliably get lefthanders out, he doesn't deserve a spot merely because he is lefthanded. That is where Solis is.
I agree with Elvir 100% here. There are plenty of righties out there who get LHB out more effectively than many LHP do. And on top of that in the case of Solis, he's been far better at getting RHB out the last 2 years than he has LHB. Splits in that regard were .224/.329 (L/R) last year and .218/.227 in 2017. He does walk RHB a bit more but also Ks them more often as well. So the argument that he should be on the roster because "he's specifically supposed to get LHB out" is just dumb. Go with your best 7/8 relievers and be done with it because chances are most if not all of them do better vs LHB than the situational lefty does. Case and point, 2018 Nats pen BAA vs LHB:
RHPMadson - 20/76 .263 (.292 vs RHB)
Kelley - 9/40 .225 (.210 vs RHB)
Holland - 2/26 .077 (.163 vs RHB)
Kintzler - 16/66 .242 (.261 vs RHB)
J. Miller - 17/73 .233 (.208 vs RHB)
Herrera - 11/38 .289 (.317 vs RHB)
Gott - 6/22 .273 (.271 vs RHB)
McGowin - 2/14 .143 (.286 vs RHB)
Cordero - 6/31 .194 (.347 vs RHB)
Suero - 18/76 .237 (.243 vs RHB)
Glover - 2/21 .095 (.282 vs RHB)
Austen Williams - 1/13 .077 (.375 vs RHB)
LHPGrace - 23/89 .258 (.229 vs RHB)
Collins - 10/45 .222 (.310 vs RHB)
Solis - 26/79 .329 (.224 vs RHB)
Doolittle - 1/30 .033 (.160 vs RHB)