They are pretty late to the party, Gamma [0] is more mature and more experienced than their McKinsey counterpart.
[0] https://www.bcg.com/beyond-consulting/bcg-gamma/default.aspx
[0] https://www.bcg.com/beyond-consulting/bcg-gamma/default.aspx
*current mckinsey data scientist who got an offer from both Gamma and McKinsey, and turned down Gamma despite being offered a higher salary.