The 'pile of cabled hardware' argument seems a little far-fetched by the way, since when do 'pro users' make a big deal out of having one or two external devices on their desk somewhere? Never heard anyone complain about that in real life.
I have this setup with a Mac Mini, the eGPU just sits behind the screen where I don't see it, and it's attached with a single TB cable + power that goes straight down into a socket. A nice benefit of this solution is that I can also use the GPU with my laptop if I would need to, by just plugging it in.
For external storage, if it doesn't get moved around you can e.g. attach it to the back of the screen, the screen I use has 4 USB-C ports at the back so I don't see why this would be worse than having the drive in a box under your desk. Or you could use a NAS with 10Gb ethernet. Plenty of options. There will always be someone who can't live with the fact that there isn't a box that has all the hardware under the desk, but that's hardly saying you cannot buy a decently powerful Mac at a small fraction of the cost of a Mac Pro.
No, my assertion is that Apple does not offer a competitively priced mid-to-high end machine suitable for professional use.
The iMac will be acceptable for some users, but not for others, because it's one-size-fits-all. In most pro audio applications, the fan noise under load is simply intolerable - you can't trick it out with Noctua fans, you can't hide the hot bits behind an acoustic partition, you're just stuck with a couple of noisy blower fans in the middle of your working environment. Lots of other pro users have similar niche needs.
The lack of maintainability is a serious issue for pro users. If something goes wrong in your iMac, you can't just order a replacement part and get back in business by tomorrow morning. A repair that would take ten minutes on a commodity box is often a lengthy process requiring specialist tools on an iMac. That's tolerable if you can afford to have a spare machine on standby, it's tolerable if you can afford to just run down to the Apple store and buy a new one, but it's a dealbreaker if (like most creative professionals) you're struggling to keep the lights on. By contrast, the last mixing console I bought was supplied with a full set of schematics; it can be completely torn down with nothing more than a PH2 screwdriver and all the PCBs and internal connectors are clearly labelled.
Apple are presenting their users with the choice between an extremely expensive and blatantly over-engineered "pro" machine, or an all-in-one that wasn't really designed for professional use in any meaningful way. There's a gaping hole in the middle of their product lineup that ignores a very large proportion of actual creative professionals.