Just posting here in case someone wonders wtf is going on with the props.
Did quite a lot of testing and finally found out that for a map to have the gravity changed for props and ragdolls, one must reload that map after changing the gravity.
However, the skill.cfg takes over the gravity put in, so one has to remove the sv_gravity 600 from it for it to take effect.
Which means… All props in the game have a gravity of 600 ingame…? While player has 800.