> But 700x28 is really the maximum tire size you can possibly fit with rim brakes
This is patently false. Mountain bikes have been running tires over twice as wide on rim brakes for decades. I had one growing up in the 90s. Perhaps you mean caliper brakes? Even if so, I currently run 700x28c on my 10yo racing bike, I don't think I'd have any trouble going up a size or two.
This is partly because of history. From the 1980s on the mores in cycling was to use skinny tires. Thus there were no road bikes with cantilever brakes anymore. Up and into the 1980s touring bikes were still available with cantilever brakes.
Between 2015 and 2020 we came back on skinny tires and wanted more than 28mm. This was the same time road cycling moved to disc brakes. Most bikes with rim brakes are still using calipers, cantilevers are not coming back. If you want more than 28mm, you will want disc brakes.
This is patently false. Mountain bikes have been running tires over twice as wide on rim brakes for decades. I had one growing up in the 90s. Perhaps you mean caliper brakes? Even if so, I currently run 700x28c on my 10yo racing bike, I don't think I'd have any trouble going up a size or two.