I agree and disagree. ScaredGirl or someone mentioned something a while ago, along the lines of, if we keep implementing 'random' or % based features in the game of elements, soon we can reduce it to flipping a coin to decide who wins or loses. Now, that statement was meant more as a flame against purely 'random' things.
But, I can assure you, a lot of people will want to know the exact numbers, the chance to miss, etc. For example, what would be the card text of a Fog Cluster? "Causes attacking creatures to miss"? "Causes some attacking creatures to miss?"
I guess people who want to know the exact numbers generally do not mind if it is clearly explained on the card itself, as long as the formula is known. The description could be something like "For each Fog Cluster, opposing creatures have 20% chance to miss." and for me it is natural that abilities like that stack through multiplication and not addition, because each Fog Cluster is a separate permanent. If it was a single Fog Cluster that grows in strength like a bone wall, I guess addition would be more natural, but as long as these are separate permanents, there should be no difference between calculating how 2 Fog Clusters stack and how 1 Fog Cluster and 1 Fog Shield stack in terms of calculation. Only the percentages in the formula would be different.
On the other hand it would be possible to have more than 6 steam lords through parallel universe, fractal, or if a false god was designed to use this card...
I think a false god with 12 steam lords, 12 quints and a lobotomizer to remove momentum would be damn hard to kill then
Or even better, fewer steam lords, but some fractals to multiply them.