I am using CrossWalk WebView and as you know it extends the app size of 25 MB more, and the app size after installation goes up to 70 MB!
One thing I need to know, CrossWalk WebView supports old devices, and make the performance much better by using a better WebView instead of the default one, but as I knew after Android KitKat Google replaced the WebView with Chromium one, does that mean that using default WebView in devices running Android KitKat+ is an alternative of using CrossWalk WebView, I mean does the hybrid application performance differ between Chromium and CrossWalk WebView?
If the performance is the same, I would use default system WebView and stop supporting old Android OS.
I found some information about the performance difference of android webview and clean cordova install here in this answer (I think this will be the most relevant for you) : Is there any real benefit using crosswalk for Android 4.4 & above?
Also while choosing you will maybe like to look at what extra HTML5 features are provided by crosswalk above 4.4 devices as in android webview above kitkat some features are disabled Resource : Why do I need Crosswalk now that Android (KitKat and later) has a Chrome-based webview? question in https://crosswalk-project.org/documentation/about/faq.html