There exists two community projects that allow you to create diagrams using higher level APIs:
Both use the core modeling facilities @philippfromme mentioned under the hood.
You can use the Modeling API without abstractions, too:
var bpmnModeler = new BpmnModeler(...);
var modeling = bpmnModeler.get('modeling');
var elementRegistry = bpmnModeler.get('elementRegistry');
// remove shape with ID 'some
modeling.removeElements([ elementRegistry.get('someTask') ]);