Don’t know the service ceiling, but from what I recall of weather could have pushed trying to top weather and when finally penetrated didn’t have a lot of performance margin left. If not proficient hand flying, having the autopilot dump it on you single pilot when potentially battling severe turbulence, icing, disorientation, panic in cabin and/or cockpit, all while nibbling at stall not a good mix.
Any flying machine can be overmatched, up to PIC not to put it there.