Clearly, the fact that Servo failed must be indicative of shortcomings in Mozilla itself, and not Rust the language, its ecosystem, or its users.
Did it fail? The servo project seems alive and well, just not under Mozilla. They decided CEO pay packages were more important.
Mozilla was the primary steward of Rust for most of the time that the Servo project was active. So if you want to lay Servo’s failure at the feet of the Rust language, it’s pretty hard to cast Mozilla as the blameless victims of… whatever it is that Rust users as a whole did to make Servo fail.
There are architectural concerns. Even when Rust proponents and cultists try to harass unrelated projects into submission, as they are wont to do.
The language surely has many cons, like any language out there. And maybe it wasn't a good fit for Mozilla products. But Mozilla the organisation doesn't really looks that great in term of governance. Given Rust is now even integrated officially in Linux kernel, I have strong doubt that the technical caveats are the main factor of misalignment with Mozilla priorities.