That's some fascinating statements, RealGun. Perhaps what would have more enlightening is to explain the differences in Brinell Hardness, how to harden cast bullets and to explain the different types of lube available.
For instance, I have two typical loads in 9mm using cast bullets, with three different lube types, such as lee Liquid Alox, non-commercial hard lube, and powder coat. One utilizes 6.4 grains of Accurate Arms #7, and reliably produces verified average velocity of 1035 FPS. With all lead types used, such as common "garbage lead" like wheel weights, I get zero leading using all lubes. The other load, arguably too hot per current published data, (the data was drastically revised by AA recently), at 6.8 grains of AA#7 slide in with a verified average velocity of 1100 FPS, and with the harder alloys like 96/2/6, I get no leading. Now with powder coating, leading is reduced to zero at almost every speed I've tried, but that is something not many reloaders use right now.
So this,
I would be cautious about references to savings with lead bullets, because 9mm is typically a supersonic round running well above velocity limits for ordinary lead bullets. The underlying truth is that you will need to cool off the caliber (load) to suit the bullet. Also, you might be better off with a more suitable barrel.
is not really quite accurate. BTW, all rounds are fired through the as-is barrel - the only barrel swap that has ever been encouraged for any handgun is the polygonal rifled Glock barrels, IIRC. Not owning a Glock, I cannot comment on that particular issue.
As for velocity limits...that's interesting. Here's the velocities I run cast RIFLE bullets, using the same better lead.
7.62x39mm - between 1776 and 1886 FPS in all weights. Properly lube and hardened, no leading apparent, even in a gas operated rifle.
8x57JS in the 175 grain Lee bullet runs about 1752 with my powder coated load, but that's because I download in respect of a 98 year old receiver.
Powder coated bullets leave no leading.
9mm is easy enough to load, and loading with cast lead bullets is also easy, once you get past the hype, and experiment on your own. Loading too hot will cause issue, but within the limitations of the material, you can make some pretty dadgum awesome bullets.
These 124 grain cast lead reloads were shot from my CZ P-09 at 10 yards two hand standing. Just as an example.