I'm surprised that the rust binary is 3.5 times bigger. D is already templated to the nth degree, what more is rust doing? On top of that D links in a whole GC whereas rust does not?
Rust is statically linked by default, not sure how D works. Rust still includes some debug features that can give you a stack trace. Size will also depend on the compile options, if LTO was enabled, how much generics were used, how much string printing was used (print is a macro in Rust that generates code at the callsite), etc. Most, if not all, of these can be resolved.
See https://github.com/johnthagen/min-sized-rust for aiming for small binary size.
This article shows a 93% size reduction, 2.7m -> 200kb, with some relatively simple modifications https://www.collabora.com/news-and-blog/blog/2020/04/28/redu....
Here is someone using Rust for a 3kb demoscene program https://www.codeslow.com/2019/12/tiny-windows-executable-in-....