I have printed images shot at close range of door knockers in St. Tropez, France, with an iPhone 7+, on 13x19 inch paper (images itself at about 12 x18) and that's about the maximum you can print I feel; with proper viewing distance all prints like very good, and hang above double french doors, but up close (pixel peeping style), you would want to make some comments, if you know what I mean. Like: "very acceptable, but could be slightly better, etc., but from a distance, they look very good." Of course the images needed Photoshop hanzaplast (bandaging).
I have the Sony RX100-VI as my travel camera, and the images can easily print on 13x19 inch paper (at 11.5x17.25 inches) with very sharp results (that Zeiss lens is truly no slouch), but I wouldn't want to push it beyond 17x22 paper prints, no matter what others may boast. Colors could be slightly better, even after much tweaking effort. You made that point well.
A 100MP mobile phone is a joke to me; your point about the issue of a proper lens for it is well taken. Marketing gimmick indeed. Pixel race in the extreme.
For more serious work, I shoot with Sigma cameras, but am on the lookout for something additional and haven't decided yet. Money is there, but decision is not there yet. :-) Xiaomi's new 100MP mobile phone: Haha, not a chance..... Fuji GFX 50R: possibly. Nikon Z7: maybe. Sony A7R-III (or II?): maybe (the iii may come down in price now?). The new Sony 61MP? Not sure. Seems like too many pixels in the same physical space. Panasonic S1R: too heavy. Same problem with Nikon D850. Hasselblad 50 MP model II? Lenses cost a fortune. But has reportedly best colors. Next year's Sigma L mount camera? (not talking about the recently announced fortepiano model). Who knows....could be a surprise camera with Sigma thinking outside the box again. That's what nice about this company; you have to admit that. Right now, we have heat wave, so I'm not in a rush. Who knows who else is coming out with surprises soon.
Good article. Thanks.