Blazor currently has to haul its runtime over the wire before it can do anything so a non-starter for anything performance-sensitive.
>1) a websocket-based HTML sync layer, basically shipping over the smallest amounts of render state from the back-end. This is as close as you get to having, essentially, a server-side rendered page that is then updated in real time.
Also it's not like you have to load the runtime more than once. So it's not that it's a non-starter for anything performance sensitive--it's a non-starter for anything that can't download a 2MB file up front (I believe their goal is to get it down to half that size) if you want to use the WASM version of Blazor instead of the websocket-based HTML sync layer version.
2. 2MB includes bootstrap CSS and they are working on getting that number down.
3. 2MB is only the Wasm version of Blazor. You don’t have to use that version if it doesn’t fit your use case.
Most people I've talked to using Blazor are in fact using Blazor server not Blazor WASM.