I have definitely heard the line that Beria was intentionally undermining the CPSU by creating an extremely hostile culture that essentially strangled the USSR, though and I guess this is either an extension of this line or it’s a direct parallel to it.

This is false i think, Beria presided over the late Stalin liberalisation which he continued after Stalin died. Though i think i can understand hoxhaist calling any liberalisation of CPSU "creating extremely hostile culture". Also it might have been even simpler, if you look at both men, Khruschev was extrememly good with handling people and influences, his career is one of a well oiled snake, Beria was far from this level so personal relations might have played a significant role.