He would attract votes in the primary, yes. But the larger issue is the permission principle in reverse.
In a crowded room, if no-one expresses a dissenting view, everyone remains silent. But if one person speaks up, that gives others "permission" to agree with the dissenter. It's human nature.
In reverse, people voting for Trump's opponent amplifies the notion that Trump is a non-thing or old hat or the past. The press will leap on the notion that Trump is history. Perception is reality. Ramaswamy weakens Trump. I think this is a strategy.