Wait, what? The AL subtiles are a huge improvement over those Viz subtitles, even though they are the exact same font - the thick black borders have specifically been added so they can be easily read against backgrounds of any color. Subtitles with thin or no black borders can be extremely hard to read when the backgrounds are very light or white. This has been the bane of subtitle readers for years and years, we have always been critical of subs with little to no outline and have been pushing for these thicker outlines, so it's a cause to celebrate! I don't care for yellow or other colored subtitles either, and I do prefer the smaller sized subtitles, so they don't hide as much of the video image. I'm in my mid 60's now but I guess my eyesight is not failing me as of yet...
I suppose the smaller subs might be more of an issue if you are watching anime on a tiny phone screen, but I generally avoid using my phone to watch anime. I have plenty of much larger screens at home to use - the 120" projection screen in my theater room especially makes anime viewing an awesome experience!