node-sass may be faster than dart-sass, but as of writing this dart-sass is the only library which implements the @use rule, which is strongly recommended over @import. According to the official sass-lang website:

@Deprecated("Use syntax instead.") bool indented

Dart is one of very few languages (and perhaps the only “mainstream” language) that is well suited to being compiled both AOT and JIT. Supporting both kinds of compilation provides significant advantages to Dart and (especially) Flutter.

Before working on Dart, the Dart team members had done groundbreaking work on advanced compilers and virtual machines, both for dynamic languages (like the V8 engine for JavaScript and Strongtalk for Smalltalk) and for static languages (like the Hotspot compiler for Java). They used this experience to make Dart unusually flexible in how it can be compiled and executed.

Dart Sass has replaced Ruby Sass as the canonical implementation of the Sass language.

It's fast. The Dart VM is highly optimized, and getting faster all the time (for the latest performance numbers, see perf.md). It's much faster than Ruby, and close to par with C++.

Dart Web enables running Dart code on web platforms powered by JavaScript. With Dart Web, you compile Dart code to JavaScript code, which in turn runs in a browser

Dart Sass is the primary implementation of Sass, which means it gets new features before any other implementation. It’s fast, easy to install, and it compiles to pure JavaScript which makes it easy to integrate into modern web development workflows.

Not many beginning developers will pick up Dart on their journey and finding new people for your mobile team can also be a challenge