That is clearly a factor in playing Rojas in situations where something like a 600 OPS is expected. Throw out the SSS stats though. Rojas will probably struggle against RHPs. He is not now, which is great, but the league really does not know how to pitch him yet.
Cave is a AAAA OF but he is what we have. We should have a better LH OF but we don't. He is a better hitter against RH pitching even if the SSS stats from this year don't make that clear. But he is also not that good. 725-750 OPS is what should be expected from him. So defense from Rojas could make a difference. Cave is a decent defensive OF himself though. Mostly a CF coming up in the minors and a majority of his major league time has been in center also. He is below average in CF and a little above in LF/RF. He is not as good as Marsh but he is not bad.
Rojas will probably play 75% of the time until he proves he can't. But there is also a role for Cave. Rob is not playing hunches. He just isn't obsessing on SSS stats and looking at the full picture of each player's talents. Cave hit better in AAA than Rojas did in AA. Those stats matter too.