D has the complexity of C++ with major drawbacks, (the stdlib was tightly tied to GC for example).
Just look at D's marketshare and its overall time on the market.
If you argument is that literally any Turing-complete language would somehow do then bravo for missing the point of basically every language besides asm.
And no, your strawman doesn't hold.
D has been on the market for significantly longer than Rust and reached 1.0 full 8 years before Rust had a 1.0 release, so not surprising at all.
But the rate at which Rust is being adopted is much faster than that of D.
Moreover Rust brings something novel to the table and even inspiring other popular languages, like Swift, in the process.
D has nothing that I'd consider novel. So personally I'll trade D for Rust any day. Luckily, we don't have to pick.
None of the other major browsers are written in Rust, there does not seem to be a huge difference in the number of security issues listed for any of those.
I once worked at a company where they wanted to build everything, preferably including their own operating system programming language and database. And all that four a payment processor, something you could probably write in any language available. Guess where that story ended?
If something isn't core to your proposition it is a distraction.