You can definitely make a webview app that starts as quickly as most native thing (sub-1s start). We used Tauri and you wouldn't be able to tell the difference.
Yes, I’ve made multiple Jumpstart iOS & Android apps that work with Jumpstart Rails and the speed is awesome.
That's a pretty simple view of native app vs web. Web will always have a lot of baggage that native apps simply won't have, layers and layers of abstractions that still needs to load.
It's true that a blank canvas loaded as a web view will start fast, though. But in practice, when web applications grow - performance tends to take a hit, and the developers also tend to be careless with resources.