It’s not so much about specialty and mainstream (not sure what that is), it’s more abut flavour intensity and solubilty.
Less soluble specialty beans can be great at 1:3, 1:4, 1:5 as long as you grind accordingly and actually like a less concentrated shot.
Historically, espresso ratios have been a range, rather than a single ratio and usually centering around 1:3.5 to 1:4.5.
There is no magic to ratio, as long as you can extract without making a sharp/tart shot, you can go as short as you can (the darker you go, the more tolerant beans are against under-extraction as roasting darker attenuates acidity). Longer ratios make balance more achievable, especially with less soluble coffee.
Historically, lungos were much longer than 1:3.3, the 1:3 lungo was a very recent thing.
Make coffee as strong/weak as you want/can and try and tie in grind and ratio, don’t look at ratio as some magic key to a magical kingdom (it just ties in to grind).