Demo needs a quicker explosion or a better radius. It’s doubtful that a simple damage increase will solve the issue (though that maybe helpful to an extent). Unless the place is really cramped as in Rival Castle’s stairway, most just sprint on it like it’s inconsequential and don’t take much damage. Case in point, I once tried to lure a demo onto two land mines but he didn’t die: he just mindlessly kept sprinting forward like the landmines were no big deal until he killed me.
In another instance, as a Shortbow on Flying Ships I saw two landmines on the entrance where you can’t jump over it. With the above experience, I just thought of spirnting back and fro to remove each of them and let my team pass. Sure enough, they did little damage to me (one did 3-ish hearts, another which I didn’t execute well did 5-ish). A defensive kit’s major defence mechanism shouldn’t be taken so lightly. Right now the kills you see in that chat from landmines are mostly from ghosts and weakened kits who didn’t realize they stepped on a mine. But I believe this kit should be a major hurdle even for those who see that it’s there.