I started powder coating my cast lead bullets for both rifles and handguns several years ago, powder coating never had to solve the problem of leading in my rifle and pistol bores because I never got leading to begin with. A properly fitted cast lead bullet with a good lube cast from an alloy that matches the velocity and pressure of the load should not lead your bores.
What powder coating does for me is it allows me to coat lots of cast bullets, size and gas check them where needed in a short period of time that can be stored long term in less than ideal conditions like my shop where other form of lube can be affected by heat or cold, PC doesn't get soft or tacky, melt of dry up over time and leaves you hands and dies clean.
As to any negatives I can't think of any, my coated bullets in both rifle and pistol don't smoke, they are just as accurate as any non-coated lead bullet I've ever used that I previously used tradition forms of lube with but now PC. Most bore cleaning after shooting my coated bullets basically entails one wet patch follow by a couple dry patches mainly to just remove any powder residue.
In general most commercial cast lead bullets coated or not are too hard with a few exceptions. I use a 50/50 mix of pure lead / wheel weights with a pinch of tin. Powder coated and air cooled right out of the toaster oven the cast bullets especially my HP handgun bullets are soft enough to give good expansion at 45 ACP handgun or carbine as well as +P 38 Special velocities. They are also fine for my 9 mm RN and TC style bullets. In rifles air cooled powder coated bullet are fine for light plinker loads or mid range velocities with gas checks applied. For HV rifle loads I powder coat my bullets an water quench them right out of the toaster oven and let them age for about three weeks before loading, I shoot these bullets out of my 30-06 at 2300 fps. with excellent accuracy and no leading. I shoot the PC quenched bullets in all my 30 cal. rifle loads in all actions types including gas operated gun with no issues.
If you want a coated cast lead bullet that give terminal performance expansion wise you pretty much have to buy a mold that will cast a bullet designed to expand, cast and coat them yourself or purchased a coated or non coated non-expanding cast lead bullet with a large meplat that creates a large wound channel.
Here is my home cast 45 ACP HP's
They expand well with my alloy and powder coating.
30 Caliber coated bullet in several colors.
50 yd. test target using the above powder coated bullet in my budget Rem. 30-06 at 2995 fps. 5 shot average.