I do think that there's some loss in translated manga, actually!

When the mangaka is creating the layout, they're conceptualizing the flow not only of the panels, but also of the text inside panels, to be RTL.

Translating the text into a LTR language without mirroring the image, makes it so that your eyes have to zig zag around a bit more, going RTL panel wise, but LTR text box wise.

Compared to the problems that mirroring the art brings, I still think that's best compromise of the options, but doesn't mean it's not an actual impact on the experience, even if a subtle one.

I have wondered before, though, about how had might it be to learn to read mirrored, RLT english. Might be a bit of a challenge at first, but would enable you to read translated manga RTL with no compromises (other than the inherent lossiness of language translation in general).

I think there’s already enough lost in translation that the text direction is the least of your worries haha