This is not true. Increases of multiple types are not multiplicative with each other. More modifiers are all multiplicative with one another (and the summed increases).
So, for a skill that has both the Melee and Physical tags,
100% increased Melee damage, and 100% increased Physical damage would be added together for the formula
Please note that the more modifiers listed could all come from the same skill tree --they’re multiplicative with eachother.
You can view the Community Game Guide to find more information on this, its a great resource. I also believe that the ingame guide goes over some of this as well.