First off, I don't buy this "rushing to production" of one type versus another. Fact is, they're ALL rushed into production including the 747 at that time. They all must make delivery or else severe penalties and loss of sales will ensue.
Second, in the Sioux City accident, the severed hydraulic lines were in the area of the elevator actuators where the lines were near termination by the user system. Unless the L1011 locates its elevator actuators and related lines in a location other than standard config, (oh, I forgot, the 1011 has a stabilator) which I understand is the reason for having the fourth hyd. system.
Actually I'm not technically fluent on the 1011 as I've never worked on one, so my opinions, much like yours carry little validity.
But I will go on and ask;
Why didn't the TriStar have two independant landing gear indication systems (like the DC10) which might have spared EAL's Flt 401 accident (no need to relamp in flight).
Why did the Tristar's wing spar have a tendency to crack, this being a major structural deficiency. I actually witnessed a Delta L1011 in the mid 80's land at EWR with this happening.
No, I don't buy into that argument. Amongst many other reasons, The DC10 carries a much greater payload than the L1011.
You're only as good as your last departure.