We had the same discussion last December or January. I think Espi's 190 K's is bad, and his 17 home runs does not begin to make up for that. He looks, to me, like a medium-sized guy trying to swing like a power-hitter. Swinging from the heels, to use an "old school" term.
The team has power hitters: Werth, Morse, Zimmerman, LaRoche, Desmond, Harper, plus Tyler Moore looking for a spot. Desmond is two inches taller and ten pounds heavier than Espi. Moore is 20 pounds heavier, and so is Harper. Morse and Zimmerman a very big guys: over 6 - 3 and 230 pounds.
Espi's 17 home runs is about three per month. That's not dependable power.
For those 17 homers, he gives a free out 189 times, or roughly 30% of the time. That is painful.
Lombo strikes out about 10% of the time, and that's with many of his at-bats coming as a pinch-hitter or spot starter. What did he do in August?
Consider a typical rally situation: runner on second or third, one out. My rough guess is that Lombo, hitting at his August rate, is more likely to drive in the run than Espi. Sure, Danny is more likely to hit a homer than Lombo, but still not very often. With that runner on third, just needing a sac fly, Espi is three times more likely to strikeout. Bang. Two outs.
Trade Espinosa? Of course not. Make him hit for average rather than try for that homer. Work on that swing he still takes at a breaking ball outside and in the dirt. He's done it since his first September...after his good first week, pitchers seemed to find that dead spot.
If he can't change, then platoon him with Lombo. Don't trade either: there is no upgrade on the market, and Desmond / Espi / Lombo are a solid infield.