Most detrivores and fungi tend to be generalist, they are not specific or picky, they will use and go after anything that's easy to decompose.
So leaf species is not really that critical near as I can tell for all the aquatic fungi and detritivor research that's been looked at.
Shrimp tend to eat these critters that are at this level or another level above the decomposers.
As far as tannins, the trace metal binding etc may be relevant in some large scale systems in nature, wetlands, river systems, but they are not in Diana's tanks, nor ours.
She and many of use add traces, whether it's in the sediment(In her case, she used extremely rich relative to plant demand Fe source sediment) while many use Flourite, or add water column ferts, which are already binding Fe using ETDA etc.
Plants are opportunistic, they will use nutrients where ever they are, sediment and/or the water column, they also leach some nutrients into the water column via the roots, and simple diffusion out of the sediment also applies greatly.
So the traces are not really influenced via tannins in our tanks in most every case.
It's nice to speculate, but that is all it is.
Folks read stuff and assume it's fact or true.
She was fairly clear about speculation in the book vs fact and she did speculate a lot.
I do also, but like her, I think what is being applied and does it support my claim. She suggested Allelopathy, but there is no evidence it exists in our tanks nor in natural systems, none.
Then I go about developing a test to see if my hypothesis might be right.
So adding activated carbon, which is the control here for leaves' impact of the tannins and water column organics can work and also works for allelopathic chemicals can be used to test this hypothesis.
If allelopathy is controlling algae growth as she speculates, adding AC to an otherwise healthy relatively aklgae free tank should induce an algae bloom after a few week's time.
However, we do not see this in non CO2 tanks nor in CO2 enriched tanks.
The test does not say what is causing algae, nor claims to do so, merely that allelopathy cannot be the cause.
Simple test to answer complex question.
The same can be applied here.
As far as shrimp and feeding: heck, add some leaves to a small bucket to the side of the tank, raise your own critters on the leaf litter.
Then add the leaves little by little.
I think the feeding on the critters on the leaves is much more what is going on, the leaves have little nutrient value for the shrimp, but the microflora/fauna is loaded.
That is really what you want there.
This way no ugly rotting leaves in your tank and you get the function.
Also, you can do all sorts of amplification to the leaves in a small bucket such as add Vitamins, proteins etc. Just add an airstone and change the water after a few weeks etc, toss a leaf in there every now and then and remove one and add to the tank.
You are basically raising live food.
I'd say that, rather than any chemicals that the shrimp like is what's going on.