IKF isn't garbage in the outfield as a spare piece. Espinal plays LF and Biggio plays RF.
None of these are optimal, but Schneider is not playing like a big leaguer right now.
IKF is garbage in the outfield, and should only be playing 3B or backup SS on this team. Also Espinal does not play LF? He has only started a total of 12 games in the outfield his entire minor league career, and the Jays aren't going to give him 4th OF time on this team based on that. Clement has more OF reps than Espinal and he too will not see time in the outfield.
Also Schneider projects for no lower than 1.4 fWAR this season (Steamer has him at this, in 308 PAs). On the higher end, ZiPS has him at 3.1 fWAR in 502 PAs. Schneider will be a very effective big leaguer this season and beyond.
Espinal played a little OF in the minors, so you could try that to get him into the lineup against LHP since he hits them well. Biggio could do it too, since he doesn't really have platoon splits over his career (102 wRC+ vs LHP, 106 vs. RHP).
No situation is going to be ideal (and this only highlights how big a mistake it was to not add a bat), but neither is Schneider while he's striking out at a 40% rate. If that's the case, they're better off plugging the 4th OF spot however they can and letting him figure it out in Buffalo.
I wouldn't even classify 12 total OF starts in his minor league career as "a little", I would call that "barely any".
In terms of Biggio, while you may be right about him not being a splits guy in his career, clearly the organization doesn't agree with us. The team has really avoided using him against LH starters more and more in recent seasons. Last season he barely saw any starts with a lefty on the mound.
Also Biggio moved away from LF permanently some time ago because he can't make reads there. With Springer I think it's similar but they just want to limit the amount of tough reads/plays he has to make in the OF while still playing him everyday in the field. Him being an RF only now is aimed at this load management wise.
You don't believe in Schneider's projections I'm guessing?