Do you agree that the latest common ancestor for all plants and animals had more types of genes than plants and animals today?
Sure, I'll agree.
If so, then don't we see the opposite of ND; rather than a slow accumulation of genes via mutation and natural selection
Not neccessarily.
Assuming, by going from the latest common ancester to animals and plants, the population loses a bunch of types of genes (to specialize into either plant or animal). If, after of slow accumulation of new genes (through RM and NS), new species of either/both animals and plants emerge, then everything is hunky-dorey. Evolution has occured like the discription in the ToE, AND, the latest common ancestor had more types of genes.
Just because genes were lost at some point in the past doesn't mean that they must continue to be lost and that no new ones can come about. If a WHOLE LOT of gene types were lost from when the latest common ancestors specialized into plant and animal, then plants and animals would have a lot of room to evolve new genes before they exceeded the original number of types of genes.
They don't however, as you seem to be assuming, have to continue to lose more and more gene types all the while never evolving a new one.