The way CRTs and modern displays, upscaler or not is too different and make results be very dispare.
CRTs do not scale, they're analogue so they just show and adjust to its screen, modern displays act in a different way and I am the first to always say that they've always have done an awful job at upscaling lower resolution content, which is why we need upscalers to get decent results, and the price on the more high-end can be eye-popping, and that's if you live in a country where you can get one of those shipped to you... If you get lucky and they're not out of stock.
Regardless, here are two direct screenshots from my Wii. In one, the game is played at 256x240, the internal resolution of the game while during gameplay using the experimental PS1 core in official RetroArch (which loves to crash), the other is on Wiistation (which plays SOTN really nice) at I suppose stretched to 320x240 so it becomes 4:3 like your usual PS1 game:
Have in mind that my capture card is far away from the great (and expensive) ones, This is my system connected to to an OSSC.
The more you look at, the more sharpness difference you can see, although SOTN isn't by far the worst example we can have. You can also notice how the spherical object at the bottom of the stairs gets more oval-like on 4:3. The biggest loser on these changes in ratio is
always the text or small UI elements for me, specially on 384 modes (like the main/memory card menus on SOTN) it gets so much blurrier and thus so much more eye strain-inducing...
...Which I guess is my entire point, now that I think about it. Me asking was not for pursuing some elitist mentality but merely that the blurring up caused by stretching causes eye-strain which can derive in other things, just like the removal of the Bilinear filter was such a massive change for quite a few of us and I will repeat, THANK YOU for giving us the option to disable it.
I don't know how much upscalers and profiles could do to improve it, as the picture has been already altered before you try and mess with their settings, but unstretching an stretched picture doesn't sound like a great solution. I could try but I don't know if the OSSC lets you change the aspect ratio in that way.
...Sorry for the rant, lol.