It may be great for you. But it will not go well when someone else needs to support it.
It might be old? GWT? Just go back to developing Web 1.0 applications and see how that goes. GWT is antiquated. I realize the churn associated with front end can be maddening, and you don't always need a Single Page App, but from a usability perspective you are really behind the times.
My first actual web app I ever built was with GWT + SmartGWT, back in 2011-12. The decision made sense at the time, because I didn't have any JS experience, and the JS ecosystem wasn't nearly as mature at the time.
Over time, though, the actual time to make any kind of change to the app became incredibly painful. The loss of the GWT DevMode plugin back around Firefox 27 hurt too.
We just finished rewriting that app with a modern React+Redux implementation, and I took great glee in deleting the entire GWT portion of that codebase. The changes have already paid off by letting us add some additional functionality that would have been a distinct pain to implement in the old codebase.
Sure, the fact that it was the second time through was a factor, but the iteration speed and codebase structure are truly both vastly improved over the original.
Another team has a SmartGWT app that they're planning to migrate in some fashion as well. Unfortunately, they locked themselves in badly by using SmartGWT's server-side black box that hooks into a DB to send data to the client. It's going to take them a while to start teasing that apart.
It amazes me how many people suggest that $2015_technology is behind the times, on a site that - aside from a javascript voting button - would happily exist in 1995.
It continues to kick everything from a productivity perspective and the framework is fantastic (for business-y apps).
People used to tell me it was too heavy weight. People used to tell me jQuery or Angular were better.
No external dependencies. NPM not needed. Might be a bit old in some places but so what.