Silverlight never had even the slightest hint of security, and no interop with JS or non-CLR (e.g. JVM) languages.
It was also comically slow and worked only in IE.
I'm well versed in security of Wasm. Much better than anything else available today or in the past, obviously still not perfect.
One of the best features of Wasm is entirely social - seems like everyone has agreed on it, finally. That's enough for me even if it was a 1:1 copy of JVM or CLR.
So says the marketing, usually pushed by those with an agenda with WebAssembly, forgetting about all those that trace back to the early 1960's and mainframe language environments with capabilities.
Lets sell old stuff as something new, never done before, rewriting history.
More recent chapter, application servers with WebAssembly, what a great idea!
I really don't think anybody is forgetting anything since people like you keep writing about it in every Wasm discussion thread since at least 2015. At this point, literally everybody involved with Wasm knows.
And people have seen what was in the past and created a modern, well-composed solution that is accepted by all major players. Excellent if you ask me. Yeah nobody has invented a new wheel here - but that's not necessary, actually it might be counter-productive to the goals of Wasm. Wasm wants to take stable, well-known ideas, improve upon the warts of previous tech like CLR and JVM and put it on 100 billion devices.
Outside of the browser, WebAssembly is still a shadow of CLR capabilities, including sandboxing.
As for the "secure" in WebAssembly, I advise a good read about the security section, specially memory corruption
https://webassembly.org/docs/security
https://www.unibw.de/patch/papers/usenixsecurity20-wasm.pdf