lower drop rates could achieve that. first off you would really make it late game. currently i can farm a 20 spawner base and get about 15k biomass an hour, enough for about 600 wall segments, which is reasonable amount you'd want to defend one side of a small to medium sized base, lowering the drop rate would def make it far more late game, as you'd need to be able to farm more spawners, and so have the resources or set up the logistics, if you wanted more faster.
lowering the drop rate would def make it more balanced for general maps. On the deathworld maps it prob won't ever be fixed, as there will be a massive influx of biomass all the time with the amount of spawners and biters around.
I'ts mainly for those deathworld/Rampant maps where its overabundant, where even reducing it to 20% of current will give you more than enough, but it will make it very hard to get in a regular game.