I think the UIWebView component that you can embed in native apps has slower performance than Safari.

I don't know the current situation, but for example Nitro was not available on UIWebView in iOS 4.3 ; also UIWebView does not do any caching by itself and doing it yourself is tricky. So this may explain why the performance of this GMail app is worse than the web app.

I understand why one would release native apps with web UIs. It's totally fine if you're on a budget. But the iPhone already has a perfectly fine email app and it also syncs well with your Google Apps account through its Exchange integration.

If an official GMail app is not better than the built-in functionality, then it's not only useless, but also affects their credibility.