Diminishing returns would definitely be the problem here.
I am a little fuzzy on this, but I think webber drones are subject to the same diminishing returns paradigm that apply to modules to when affecting the same stat.
That paradigm is this:
First module that affects a specific stat (usually the one that affords the largest bonus): 100% of that module’s bonus is applied.
Second module that affects a specific stat: ~87% of that module’s bonus is applied.
Third module that affects a specific stat: ~50% of that module’s bonus is applied.
Fourth modules that affects a specific stat: ~20% of that module’s bonus is applied.
So in your hypothetical scenario…
- you use a a Tech 2 webifier on a target (cuts the target’s speed by 60%)
- you send out webbing drones on the target
Each webbing drone has a web strength of 5%. So that means the first drone will apply only 4.35% webbing on the target, the second will apply 2.5%, the third applies 1%, and the last two drones are basically “wasted” in the sense that they are not really contributing any meaningful web strength.
(NOTE: Someone should probably check my math on this!)
More than all this… in EVE, bonuses stack multiplicatively (see, they are not “added” together).
What this means is that your total amount of webification will be somewhere in the range of… 65%?
ECM drones would be a better choice. 