If you consider that Amgen spends around $3 bil / yr in research cost I would think paying $10 + bil on a company like Onxx might be the smart thing to do if you look at what they've produced over the last 10 years.
When AMGN bought MITI, blinatumomab was already in two pivotal trials, one in rrALL, one in MRD ALL - they should have results later this year and early next year respectively as originally planned. The only new trial AMGN has initiated is in rrDLBCL, which was also previously planned before buyout.
By the way, I definitely think companies like AMGN would be better off by buying high quality small to mid cap biotechs like ONXX, MITI - some commercial stage some development stage - than buying back stocks.