I used to have these figures written down somewhere when I was flying the things, but the figure of 5% climb gradient, at MTOW, ISA +25, Sea Level, comes to mind.
The B200 is a very capable aircraft when flown accurately on one engine. But, an engine failure at or just above rotate requires some pretty precise flying to get away from the ground safely.
Until one is put in such a position, then I'd be hesitant to say that "he should have been able to fly away on one engine".
RIP to all those onboard.
morno