Kookoo Yoko turned his fortune into an even larger fortune and did a great job with their son. So she did something right.
I think she was instrumental in breaking up the band, that's all.
Yoko is a homewrecker who financially froze out Lennon’s son with his first wife (Julian originally got some measly trust fund - I think he later got more after fighting with Lennon’s estate). Yoko may have business acumen but she is an utter witch.