Most development time isn’t typing code but actually architecting the solution. You will go through multiple iterations to get your UX right. Lots of things like graphics, GUI mock-ups, database design, file formats can be reused.
In cross platform development one too often ends up wasting time on problems introduced by buggy layers on top of the native frameworks.
Every time I have compare my development speed using native tools vs a lot of the cross platform web stuff, native wins hands down.
But it depends on where your skills are. If you are more skilled with web technologies then your experience will likely be different.