We built an Amiga-like OS for a set top box. We didn't steal a single line of code from AmigaOS, and we didn't try to sell as "the new AmigaOS".
The MorphOS people did not not-do any of those things.
At the time MorphOS was started Amiga OS was dead. They created something along the lines of Haiku - a better recreation than the original. OS4 was started after MorphOS. I don't know the time difference but IIRC it was several years.
More importantly, the MorphOS guys have always vehemently denied that they stole any code.
There have been plenty of allegations and even threats of legal action, but I don't believe anyone have ever produced anything to back these allegations up.