One thing people have to understand about "A Night to Remember" and the 50's "Titanic" for that matter was they were more of a vehicle for the actors of the day. Kenneth More, who portrayed Lightoller, was one of the biggest stars, of course he was going to have a meaty role.
That's perfectly true though there was also a bit more to it.
In the documentary on the making of ANTR, MacQuitty and Lord mention how before the screenplay was written they decided it would be for the best to have that one pivotal character who was likely to interact with the everyone and be in the thick of the action. So they chose Lightoller - Walter Lord agreed with this so long as the incidents portrayed were still based on reality.
As a result, Lightoller is part of all these scenes based on documented reality but which happened to the other officers:
The boats are being prepared and Ismay starts to annoy the crew but is brushed off (Pitman)
Ismay interferes in the lowering of one of the first boats to be lowered and is told in no uncertain terms where to go (Lowe)
Brief panic at Boat Fourteen and shots fired in the air (Lowe)
Collapsible D is lowered (Wilde)
With the assistance of Moody, trying in vain to get Collapsible A off the deck (Murdoch)
Don't know why they never gave Murdoch a Scottish accent in ANTR. Could have cast a young Sean Connery in the role