Yea, as far as I know, it historically was basically just MRA doing it with any real consistency. You'd occasionally have a coach that went out for players, but you didn't have boosters that were consistently willing to pay other people's tuition. You might have one here or there pay for a kids friend/teammate outside of school sports, but if anyone was doing it consistently, they weren't making enough of a difference for people outside of their local area to know about it. Even now, I'm not sure it's happening much outside of MRA, JA, and I guess Hartfield. OTher than those, I think the recruiting is more "wooing". Coaches and parents making them feel welcome and wanted, but not actually throwing money at them.
Yea, I think the public v private cuts both ways in competition. Public schools are generally going to have access to better athletes if the private school isn't recruiting, but the private schools aren't going to lose very many good athletes because of poor home environments like a lot of (most?) public schools do. I had a coach from a not poorly thought of school district tell me there was more raw talent walking through his halls whose home environment and upbringing left them unable/unwilling to do the minimum things required to play football (e.g., show up to practice even when they feel like it, not talk back to the coach, etc) than he had on his team. It surprised me because it wasn't JPS we were talking about, and I also thought playing football would be so desirable that even most of the roughest thugs would try to do it if they thought they could get playing time.