At best RD may be telling a 1/4 truth. While true many slaves learned "valuable trades" (John Hemmings, Sally's half brother, became a master Joiner training under white master craftsmen) they were still slaves. There was no way they could go out on their own to obtain jobs. Most likely they were "rented out" to other farms and plantations and their masters reaped the riches of their training. Not to mention separating workers from their families for months at a time.
Even after slaves were emancipated, a free black finding a decent paying job in a white man's world was fairly unlikely. Heck, even into the 70s and 80s minorities usually received second class wages.
I highly doubt the "anti-woke" crowd wants to see this taught in their schools because their privileged white kids would feel bad.