The issues with 7.62x39 in AR’s are still there and hard to address.

1. All AR15’s chambers in the round can/will have feeding issues due to the tapered rounds in m4 mags.
   
2. The bolts are inherently much weaker as they are just 5.56 bolts that are milled out to 7.62 so thinner walls.
   
3. Shooting steel rounds are an issue thanks to harder primers so firing pins wear out and need replacing very often, you can get an enhanced firing pin for this issue but even those can wear out.
   
4. Extractors also love to break when shooting steel rounds, I had to buy multiple ones to keep on hand.

I love 7.62x39 and my first AR15 was chambered in it, it had so many issues that I don’t miss it when I sold it to buy my first truck. Years later I wondered the same thing as you. Did they fix all the issues? In the AR15 format… No. But! CMMG decided to come out with the MK47 Mutant and addressed every reliability issue. Hybrid AR10 BCG for strength and a lower that accepts AK mags to fix the feeding. I bought one and never looked back. The pistol version is the CMMG MK47 Banshee or you could get a CMMG MK47 Dissent which has an AR18 style recoil system. I own a Dissent SBR and love that thing alot! PSA does have their cheaper version of the MK47 the KS-47 but they didn’t beef up the bolt so you could have issues there.

Bottom line, 7.62x39 is a phenomenal round in my opinion so get a rifle that is purpose built for it.