Earlier quoted context omitted.
No. This isn't fixed by open source. Open source projects also do binary releases (see brew cask), and those need to be universal as well. Someone needs to build those universal binaries, and homebrew has decided to be incapable as a platform to do that by refusing to ship universal binaries. It is kinda mitigated for end users if you only run an x86 homebrew for the foreseeable future and never compile any software…
Cross-compiling is a need that almost no user ever has. The only legit need on macOS was for a long time iOS only and now, the two supported CPU architectures. But that is covered by using XCode. There would be now need for a Apple Homebrew to use or provide universal binaries. Homebrew's design is for providing tools for the need of the single user of the system (it doesn't even work well in a multi-user environment…
I'm speaking from personal experience about what is broken about homebrew's developer tools for a software developer building and using lots of existing open source software for Mac. Please don't respond further unless you are absolutely confident your position is in good faith and supported by personal relevant experience.