Justin,
I’d doubt you’ve harmed any of your records playing them a few times at 2g. But if the past owner was careless about that, what else was he not paying close attention to? If that cartridge has been run for hundreds of hours at 2g it probably isn’t performing too well any more. I don’t see the purpose in repeating the previous owner’s mistake and setting it back to 2g. The only real rule is the manufacturer’s recommendation.
I was going to point out to the CD fans that it’s possible to spend thousands on a CD player/DAC and still find that vinyl involves you more. I bought, after many expensive errors an Ayre C-5xe, their last multi-format disk player. It cost about 8kCDN in 2005, and it’s still the best CD/SACD player I’ve heard. But I choose to play records rather than CDs or SACDs. And at that time I was using an RP3 and a Shure V15 VxMR (maybe a quarter of the CD player's cost). That made me go full time back into vinyl. But then I saw you had proved it for yourself with your brother’s turntable.
I’d replace that cartridge if I were you. Something like a Nagaoka MP-110 will cost you $150 and should be enough to do the job. Buy a Spin Clean for $80 and use it. Those would be my recommended first steps and I’d want to know the results before spending a penny more of your money. We don’t know for sure if the rest of your bargain Sony is performing as it should yet.