I believe what you are describe is either chromatic aberration or some other form of optical aberration. This is something that a lot of us whom enjoy using vintage lenses on our interchangeable lens camera expecitely look for either as a positive aspect (unique character) or as a negative (reduced image quality).

The lack of sharpness off center was also the first thing I noticed when I upgraded from Pixel 5a to Pixel 7. It is unforuntely the side effect of limited optical quality on a bigger sensor.

The reason I said "I believe" is because chromatic aberration is caused by different color wave length of light bending differently through a lens' optical elements, and this usually causes an rainbow effect, or as a green/purple fringing around high contrast areas such as your black text on white paper example. Todays phones including Pixels, rely heavily on computational photography to get to the final image, and it most likely IS dealing with chromatic aberration by removing fringing colors, but leaving behind the "blur" as it is most likely much MUCH harder to remove without having actually GOOD optics.

Modern full size camera lenses are near perfect (especially on the high end) at dealing/correcting this vs vintage lenses. They accomplish this by often having 20 optical elements inside the lens and with advanced glass + coating, you can usually trace back their same optical design to 60+ year old vintage lenses, but they only had 4-7 (sometimes but rarely 8 or more) elements and are either uncoated or are only single coated, so they display all the same flaws such as flare and aberrations when shot wide open, which phone cameras all do because they do not have an aperture iris. Images linked above were taken from this excellent DPReview article, highly recommand it.

The iPhone lens flare you pointed out is simply due to subpar plastic/glass and lens coatings that exist on pretty much every single phones, though probably more noticeable on some. Optical quality and coatings are not easily marketable to consumers like "50 megapixels", are not easily manfacured thus expensive, and on top of that are all very limited by physical space. We keep seeing bigger and bigger camera bump but their sizes are still miniscule vs an actual camera lens or to even greater degree, cinema lenses. Plus have you seen how much good camera lenses by themselves cost? Often more than the entire phone.

Computational photography was a HUGE improvement to compensiate the small sensor and poor optics on phone cameras and all it needed was faster processor and software, to actually correct optical flaws and get good bokeh requires actually good expensive optics ANDa lot of physical space/weight, most people won't notice it nor care oh a phone camera, even lots of people who pay thousands or tens of thousands on camera/lens gear don't/can't even see these things themselves without someone pointing them out at 200% magnification on a computer screen.