Sadly, I don't see Gimp ever competing with Photoshop. It's not necessarily a feature parity thing, nor is it a mind share thing. It's as you've said - it's not built by creatives to be the best possible tool for many types of design.
It's truly a shame, because for years Adobe slept on different aspects of digital design, and there was a true opportunity to build a Linux-first tool that made things like Web Design so much simpler. It's an unpopular opinion, but Linux window managers have always lacked creative input. There has always either been a design-by-commitee, or a design-by-engineer feel - and this is reflected in how poor Gimp and design tools are in the Linux space.
In reality, Linux could have the best photo editing and design-specific tooling, but sadly the tooling either lacks a creative touch, or lacks features that are truly needed to be competitive.