Rust is - by design - antithetical to pretty much every idea of rapid application development paradigm Delphi/VCL and to lesser extent Qt adhere to.
It doesn't matter how many of Rust UI toolkits there are. Consider that there are a lot of Rust game engines, and pretty much zero games written in it, because even C++ gives you better trade-offs in that particular space.
IMO it's not ideal for Rust to have only Rust specific toolkits (at least they need to have other language bindings)
I've tried using Qt (non QML, using rust-qt) last week... initially things were looking fine (despite unsafe everywhere)... but I found quickly that I need unsupported things (deriving from C++ classes), and the project isn't really maintained anymore, so I'll need to so some low level work myself if I want to proceed.
What's interesting is the speed at which Rust UI toolkits develop and maybe even mature.