Thank you so much for your reply, Rene. You have given me renewed hope that the API will be able to satisfy our performance needs. Right now I am working with a dataset of about 13,000 polygons, comprised of 2.4 million points. I'm not sure if that sounds unreasonable, but I have found a few other maps frameworks that can handle it no problem. I just don't like the others as much in general, and I am really hoping to make ArcGIS work because it is the overall best maps API I have found.
Does version 4.10 of the API use WebGL when rendering a FeatureLayer with GeoJSON features in a 2D MapView? This blog post, entitled FeatureLayer rendering: taking advantage of WebGL, from September 2017 indicates that, as of version 4.5, WebGL is used when rendering a FeatureLayer with hosted on AGOL and that WebGL support for features loaded on the client side was in the pipeline.
This new technology is currently only available when visualizing feature services hosted on ArcGIS Online. Support for client-side feature collections and non-hosted enterprise feature services will be supported at a later release.
Has the API since implemented a WebGL solution for client-side feature collections. If not, is WebGL part of the performance upgrade that you mentioned is coming in 4.11?