Reading all of that it sounds mostly like a dev who has spent 20 years doing things the C++ way wasn’t comfortable learning something new. Like basically they’ve been using horrible design patterns that Rust bans because they’re horrible, and instead of learning better approaches they just say Rust is bad
If were just a personal project that they’re building entirely on their own then sure, go nuts and do whatever you want. But they’re trying to gain adoption, asking for contribution, and wanting to replace other browsers. At that point it’s no longer just a personal choice if you’re asking the community to invest their time and money into it with you