The out-of-the-box models in Production Mapping and Defense Mapping may not meet all of the requirements for maritime data but you should be able to use the models to create an initial generalized result and you can build additional models to further refine the results.
In ArcGIS Pro, the generalization capabilities consist of geoprocessing tools that perform generalization operations like thinning and simplification. These tools can be combined together into Model Builder models or python scripts to perform multiple generalization operations on a type of feature. Because these models can be quite complicated to create, a set of generalization models are provided as part of the Production Mapping and Defense Mapping products that contain the most common types of generalization performed on topographic data.
The generalization models contain a fixed set of operations but are configurable so you can determine which operations to perform on each type of feature. For example, with islands you can choose to aggregate multiple small islands into a larger island, eliminate the island into surrounding features, and\or delete small islands. Based on your description you would likely want to perform the aggregate but not the eliminate or delete operations.
When performing generalization you can use any geoprocessing tools to create your own models. So if there are additional operations you want to perform on your data, you can build a geoprocessing model or python script and it can be added to the out-of-the-box operations when running generalization. For example, with 3.1 of Production Mapping there is now a geoprocessing tool to enlarge features, however, it is not used in any of the generalization models. For islands you could add this tool to a model to enlarge any small islands so that they are large enough to visualize at the output scale.
While the out-of-the-box models may not meet all of the needs for maritime data, hopefully some of the models will be useful as-is or at least as a tool to learn how to construct models for maritime generalization.
