On the highest level, yeah, it really is just more modern.
In practice though, its also flexibility. GWT shoehorned you to do certain things a certain way and only that way, where as Blazor only limits you based on what calls and modules can be safely converted to run against the WASM driven runtime. Which means you aren't limited to a specific list of ways to solve a problem, its more (and increasingly so) flexible than that. So for instance, GWT has specific widgets[0] that you should use to represent the use interface, Blazor doesn't limit you to just Blazor compatible widgets (there are some though, because at some point the abstraction runs out of juice). You can use regular conventions and classes too, like the normal .NET HTTP client stack, regular data classes etc. You can also re-use Razor components, most of the time.
To be clear though, Blazor isn't a panacea, it has its own caveats and downsides, however I think its really innovative in terms of concept and execution. For anything behind a login its a pretty sensible choice IMO. I wouldn't go making your marketing / info / purely static pages with it though. server side rendering or pre-rendering is a much better choice there.
Also worth mentioning, on top of all that, is Blazor can cross compile to native applications too, like iOS and Android, with (largely) the same codebase.
In practice though, its also flexibility. GWT shoehorned you to do certain things a certain way and only that way, where as Blazor only limits you based on what calls and modules can be safely converted to run against the WASM driven runtime. Which means you aren't limited to a specific list of ways to solve a problem, its more (and increasingly so) flexible than that. So for instance, GWT has specific widgets[0] that you should use to represent the use interface, Blazor doesn't limit you to just Blazor compatible widgets (there are some though, because at some point the abstraction runs out of juice). You can use regular conventions and classes too, like the normal .NET HTTP client stack, regular data classes etc. You can also re-use Razor components, most of the time.
To be clear though, Blazor isn't a panacea, it has its own caveats and downsides, however I think its really innovative in terms of concept and execution. For anything behind a login its a pretty sensible choice IMO. I wouldn't go making your marketing / info / purely static pages with it though. server side rendering or pre-rendering is a much better choice there.
Also worth mentioning, on top of all that, is Blazor can cross compile to native applications too, like iOS and Android, with (largely) the same codebase.
[0]: https://www.gwtproject.org/doc/latest/DevGuideUiWidgets.html