The extra ram in 1tb pro is just there to keep the larger storage performant. It’s likely there is no real world difference between the models (iirc there was a few tests done) so thats a total waste unless you need 1tb. As next to no-one has 6gb, pointless developing towards that target.
Double kicker is that by the time the ipad does get more ram, devs will likely target the extra capabilities toward the new models so the old one with extra ram won’t even benefit then either.
The 6GB is available entirely for the iOS to use. And yes there are also specific applications that allow the 6GB of ram iPads to add more layers.
I’ve beat this horse to death. You can use the 6GB of ram.
The iPad Pro has 3.7GB of available ram. The 1TB model has 5.7gb of available ram.