But with a Seneca it can happen 10kt before the stall, even with the centre of gravity well within limits.
That becomes a certification consideration. Though I have not flown a Seneca, I have flight tested a number of other "stabiliator" Pipers. Yes, stabiliators will stall themselves at high (up pitch command) stabiliator AoA's. This was a factor in the early Cessna Cardinals (also with a stabilator) being required by AD to have slots added to reduce this effect. That being said, the stall may be defined as an uncontrolled pitching down, or control held to the pitch up stop for three seconds. I was doing that testing in a Cessna Caravan last December, slowly apply full nose up elevator, then hold it there for at least three seconds, and see what the plane does.
So an attentive pilot must maintain flying speed. This pilot did not do that, he did not maintain enough speed to flare the plane to arrest the rate of descent. Sure, shut the engines down to save severe propstrikes, I would too, but then make sure that you fly the plane into the flare, to preserve speed with which to flare!