I've heard this many times.....and I think it has to do with timing more than anything. From oct 2001 to probably 2007 (when a few majors started to hire), a lot of major pilots had been laid off and not recalled so corporations may have been reluctant to hire them. Granted, a lot of those guys had friends that could help them out (perhaps old, pre2001 military/previous job friends). The good corporate jobs were super tough to get, so those doing the hiring could easily make a statement that they wouldn't hire major pilots since they had plenty of well-proven, perhaps typed pilots to hire.
I don't think former 121 (in the corporate world) has the same meaning/image now as it did then.... But it's more of a function of pilot availability.