"no way to define the layers, the loss function, or any knobs to play around with the network". -- This is the point of the service - to enable the (vast group of) users who want to custom-classify images of X/Y/Z without having to understand the difference between momentum and learning rate, or hire people who do. If you do want full control of the model, you should look at Deep Learning as a Service - https://www.ibm.com/cloud/deep-learning
Maybe you were referring to the _demo_ of custom training, here: https://visual-recognition-demo.mybluemix.net/train ? The demo only classifies using one classifier at a time, but the API can do multiple at once.
Not sure what you mean here - With Watson Visual Recognition, you can train a set of custom classifiers from your example images.
Then in a single API call, you can upload a batch or single image and get a score for each image for each class in all your classifiers.
There are limits to the size of the ZIP files you can upload, that's true.
"no way to define the layers, the loss function, or any knobs to play around with the network". -- This is the point of the service - to enable the (vast group of) users who want to custom-classify images of X/Y/Z without having to understand the difference between momentum and learning rate, or hire people who do. If you do want full control of the model, you should look at Deep Learning as a Service - https://www.ibm.com/cloud/deep-learning