Aside from the lifeless acting, half the movie felt like dead time, as secondary events were taking up most of the duration with slow pacing, leaving very little for the main plot.
For example, calculate how much time was wasted on trying to rescue Laureline from those aliens by side tracking for a shape shifting stripper, when there was a hatch right there in the throne room. For all the time Valerian wasted on trying to sneak in and not cause a mess, he ended up causing a mess and escaped through the hatch. Why didn't he simply use the hatch and be done with it?
So we can have a completely useless strip dance. Not to mention how we are also supposed to care about the stripper afterwards, when in effect she was removed from the plot exactly when her purpose was fulfilled.
You're not wrong there. I liked the stripper, though. I know she was an alien, but my first thought was that she brought a bit of humanity to the screen finally (before being removed). Yes, the plot was a mess.
I might as well add the plot armor of Valerian having the soul of the dead alien inside him, so the rest of them will not oppose him once they meet and the story can conveniently move in his favor without having to kill any of those victimized fellows. For a plot point that was foreshadowed in the beginning of the movie, he dismissed its importance early on, and the aliens on the multi dimensional bazaar did not do something about it right away.
And then it's the plan of the human general to hide the truth of the battle. How exactly would he do that where there were thousands of soldiers fighting on both sides? How do you hide the destruction of a planet by erasing footage and killing a couple of staff members? There were way too many witnesses, enemy side included.