Its not about falling and doing damage to yourself but having the skill to attack the other worm and get fall damage. If fall damage was slightly higher and if in 8 turns you get 6 fall damage every turn, you can make up a full attack and do 47 extra damage. So you can make up for an attack you missed or take the lead by an attack.
I don't know how you can argue that more fd wouldn't add more skill.
That's the other side of the medal. Giving FD does take skill, and multiplying the damage does increase the importance of '51'-drops, but on the other side, it's also a game decider that will ruin any chance of getting back in the game when you fall on the middle or the top of map.
I think that disadvantage greatly overrules the advantage. Whether you do 3 or 6 fall damage per turn extra, in either case it's enough to take an advantage over your opponent. Yet, when things go wrong and one of the players takes an ugly fall... "consequences will never be the same"
For me this is like putting 5 power clusters in mole shopper. Compared to the other weapons the cluster is equal to a banana, but instead of 1, you get 3. 3 clusters can take out 75% of the team in one shot, that makes them way overpowered and shakes the balance of the game.
Likewise in Roper, double FD-damage might give up to 150-200 damage in one single turn. And that doesn't sound like a balanced scheme to me.