Politics aside.... The Legacy amps don't sound "Legacy" from what I experienced. They sound somewhat vanilla and lack the throatiness of the RB series. They sound modern with a less than grunty distortion circuit.
"Boost" - really had/has something special in the RB line.
The other 2 new GK class D amps are already modern and super flexible from the looks of it.... the "Legacy" should have been more simple with a meatier tone. YMMV.
I would disagree on all counts. I spent about 10 years playing 800RB/Mesa Diesel 215 combo for reference. I've owned the 800 and 400RB's over the last 10 years as well, so I'm familiar. I'm still sorting out how to best use the distortion circuit, but that is where the extra grunt and where the "rails" feeling comes from so far for me. Although I don't need to distortion circuit to get nasty. It's a very capable amp and I wouldn't describe it as vanilla. It's a GK and it has a lot of the aggressive stuff I loved about the RB series. How much time have you spent with the legacy and the RB series?