The fact that you can only upload 150kb .svg images (and have to go through an actual website to upload them, what is this, 2008?) and that there is no internal layer group editor makes this something I can't agree on. And at the end of the day, having to work with the limitations of the GTS editor means trading the tools of the Forza paint editor with those of dedicated software like Inkscape or Illustrator. Go ahead, tell me it's easier to draw with Bézier curves, I'll just laugh in your face.
Personally, I think there are other things that T10/PGG can do without radically altering the editor (or having to implement yet another layer of content moderation) that would benefit painters way more.
The first thing would probably be to add the possibility to share unlocked decals, as it was back in the Xbox 360 days - Gran Turismo allows everybody to freely use the decals uploaded to their servers, and other games with livery editors (like Ride 4, which nobody seems to be talking about) also allow players to share liveries making use of downloaded layer groups.
Extending the paintable area to the car's windows should be something else to look into for Forza Motorsport, but it would probably be a brake caliper situation if they tried to implement it in FH5. And adding proper layer masks and the ability to choose specular of each individual layer would likely be hard to implement, but it would absolutely be worth the hassle if they could.
But at the end, I'm skeptical any of that will ever happen - mostly because T10/PGG seems to direct their action with surveys and focus groups, instead of asking content creators vis-a-vis what kind of improvements they'd like to see.
P.S. calling people "elitists" simply because they like a thing won't win you many friends, nor convince a lot of people about the validity of your arguments.