Seriously. It's implausible to think a Klingon could kill Odo with a sword. But, since the writers purposefully avoided going into detail about the mystical mass-altering magical morphing security guard's anatomy when he's in humanoid form, it's not impossible. The director/writers probably just went with which weapon looked better.
Actually, it is
impossible, as proven in the episode Chimera
. The only reason they were able to try to put Laas on trial (which btw, is in and of itself another ludicrous plot contrivance...Klingons wanting a trial for a death regarding a fight they started...
) was because everyone knew it was impossible for a changeling to die or any any way be harmed from a bladed weapon.
And Photon, condemning the entire series as having FUBARs and lazy writing because of something as minor as Odo getting cold-cocked in an early episode is a tad melodramatic. And thinking that giving DS9 Star Trek XI treatment would reduce plot inconsistencies is utterly laughable. DS9 is thousands of times more consistent than that movie, entertaining though it may be.
Photon wasn't condemning the whole series, rather what he is saying is that all the fight scenes in the series could have been thought-out and executed much better; which indeed they could have.
I don't think he was meaning to compare Trek XI's (lack of) quality to DS9 either. I think he just meant if there is a DS9 movie, then he wants the fight scenes improved for it.