The majority of my records are old. Those that were in the house when I was a kid were treated pretty dreadfully, being played on an old Garrard radiogram and then a Philips portable player. Stylus changes only happened when the thing would no longer play! And yet, right from my first RCM I found they could sound surprisingly good, and with better RCMs the improvement continues. I can't cure a scratch, sadly, but if a record isn't scratched it will usually be as near silent as makes no difference. The fact you say your new records sound great must give you some insight as to what's happening, no?
You may be right that your old disks were mistreated far more badly than mine, and they are damaged. The only way to know is to get a couple cleaned as well as possible and see if they improve. If your RCM is "perhaps not the best," have you the possibility of getting a couple cleaned by someone else for a test?