Lead is softer than barrel steel, so it'll deform before it will wear the barrel out regardless of the shot size.
If you do have an older thin-wall barrel with a tight choke, the choke can get peened out just like with steel shot...but it'll take many many rounds.
Heck, I know guys that have shot forster-type slugs through their old full-choke guns for years with little or no damage.
Sounds like internet commando mall ninja talk to me.. Soft lead cannot wear ordnance grade steel unless its coated with an abrasive (think lap).. It just isnt possible. Its why you see so many 100 yr old .22s with new looking bores.. Cuz lead cant wear out steel..
Time to find new friends or to start disregarding anything coming out of the mouth of your source. There is an awful lot of things that people know that just ain't so. Common sense will eliminate most of the garbage but some of it sounds so reasonable it doesn't hurt to ask and good on you for asking instead of passing on bad information.