Colleagues who have flown the 412 in firefighting role in Cyprus agree that with a full or even partially full bucket, OEI performance is not possible, other than to take you to the scene of the accident.
It is not unusual to be pulling 100% Tq lifting the bucket and having to make a very gentle transition because there is no excess power available.
It looks to me as if he slowly inches forward to begin the transition and realises he is up to or exceeding his Tq limit and tries to recover to the hover when the malfunction occurs.
We all know that if a mechanical element is going to give up the ghost it will do so under maximum strain which is where he would be in that scenario.
The amount of yaw is tiny, as you would expect from a single engine malfunction rather than the very large yaw you would experience with either a driveshaft breakage or a double engine failure.
He droops the Nr by trying to cushion the water entry at high AUM on one engine and, since he doesn't release the bucket, he is now attached to a large sea anchor.
He has also just put the TR into the water with all the shock loading one might expect - I certainly wouldn't be trying to fly again in those circumstances.
He is low over the water and has an armful of power, presumably single pilot, so I think it is unrealistic for armchair quarterbacks to suggest he had time to pickle the load - especially if, as I suspect, he had a freewheel let go and was trying to work out what the failure was whilst preparing for water entry.
I've done plenty of firebucketing at MAUM, albeit on a Wessex, and I think he can consider it a job well done just surviving a malfunction in those circumstances.