I just don't think most teams/analytics department see it that way. Though, to be fair, they also see things that we have no idea about, in terms of swing paths and types of pitches thrown by the opposing pitchers.
But either way, last year Rojas had a .633 OPS in 257 PAs against RHP and .526 OPS in 106 PAs against LHP. In 2023 it was .760 in 90 PAs against RHP and .788 in 65 PAs against LHP. That just doesn't seem like any useful amount of data let alone definitive data. As with all part-time players. When a guy gets 5-600 ABs for three years and has reverse splits for three years, that's different.
But also, more tellingly: last season he had a .560 OPS in 234 PAs in games where there was a RH starting pitcher, and a .677 OPS in 130 PAs in games where there was a LH starting pitcher. So to me that says he starts against LHP and perhaps he just got a little lucky (and unlucky) against a few relievers.
The one other thing to consider is he hit RHP better because he saw them more. That's always been a big part of a LHPs advantage regardless of which side the hitter comes from. But it doesn't seem like the Phillies are any more eager to see Rojas hit more than they are to see Marsh hit more against LHP.