There's been a lengthy discussion in the past about dropping composer in Flarum. This discussion took place behind closed doors with contributors and core developers. Initially @Toby and @Franz both strongly believed in abolishing composer but gradually agreed that we're building a quality-first product. It's a tough discussion, feel free to search here on discuss about that topic if you want to know more.
As a consequence we decided to rely on using composer to guarantee underlying dependencies and server requirements are met. Shared hosting has also changed since Flarums' inception; more resources, faster PHP version releases and terminal access have become more common.
Even though I'd like to praise your optimism, I'd like to point out that we've already settled on delaying stable to early next year with a Release Candidate potentially being shipped at the end of the year. However, we still have quite some work ahead of us, especially if we want to tackle some of the minor issues along the way. Revamping the whole logic of composer or installer would be quite impactful and might cause delays which I'm personally no longer willing to accept.
