Caveat: this is information only and refers to modern glass. Make of it what you will.

My wife and I take underwater photos. My wife's dome port, made from a relatively hard mineral glass according to the manufacturer, got scratched last year (Scottish granite I suspect!) - a little under 1cm long and easily felt with a finger nail, peripheral scratches/scrapes too. I decided that rather than leave it as is, I would attempt to polish out the scratch myself. So armed with a Dremel fitted with a polishing felt tool and some jeweller's rouge I have been slowly, for short bursts, polishing the affected area. So far some of the peripheral damage has gone. The main damage is reducing but very slowly. I'm being extremely careful not to allow the area to heat up - if I can feel any warmth developing I stop and leave it for an hour. Differential heating of glass can shatter it - I had a professional firm try to polish a scratched dome port some years ago and it did shatter - they only undertook to try at my risk.

What's my point? Well if an softer, uncoated lens has a significant scratch which causes problems then it might just be worth attempting to polish it out. Dome ports are simple lenses though and a relatively small area with a very slight difference in its curvature is unlikely to be problematic. I'll report when I've finished polishing the scratches out - may be a few weeks away - but it seems to be working so far.