I think even worse would be making large shifts, playing angular lines. I would have trouble because each string would have a different shift length, I prefer unlined board, and I don't like having to look at side dots all the time.A regular fretless always has an exact lateral move to the 4th on the next string up or 5th on the next string down so I can pretty much always use the same fingerings regardless of the register I'm playing in (of course the distance of other intervals shifts, but that is easy to get accustomed to), on a multiscale that point is always different dependent on where you are on the neck (sometimes it will be in front of your current position, sometimes behind) requiring different fingerings in many cases. As @Wasnex mentioned, being able to play quick and complicated lines on a fretless requires knowing where to put your fingers before you play the notes, you can't really depend on being able to slide into notes- and on a multiscale that would shift significantly depending on where you are on the fingerboard (sometimes a 7th will be where a 6th would be on a standard scale, sometimes it'll nearly be a full fret up relative to the standard scale). I don't doubt that I could get fluent playing a multiscale fretless, but I think it would be a huge time investment!
Does a multi scale fretless even come in unlined? I don't think I've ever seen one.