Alright, I think we'd have to find out how much SH was able to write what he wanted. I mean, not just plotting but the line by line dialogue. If DC was so controlling that he even managed to interfere with and ruin (in Sam's view) that, SH can certainly be critical of DS without indicting himself in the process.
On the other hand, if DC controlled plot, but left writers free to try to make that plot come alive with whatever lines they wanted to write.... then SH is perhaps directing inner criticism outward. I'm a total amateur obviously, but I would think that it's the responsibility of the writer to take what he's given to work with, and make it work. I think good writing in a disappointing plot is possible.
As for his Frid comments, I'm pretty sure he wasn't putting NODS on a pedestal. I think he probably meant that JF shouldn't have been so "proud" or "choosy" about his roles, considering that (in SH's opinion, not mine), Frid wasn't destined for a glorious stage career one way or the other. He seems to base this on JF's poor memorization of lines. You know, in the theater, they actually let you perform the same lines night after night, rather than making you memorize new ones every day!
My memory is considerably worse than Mr. Frid's. My life in the theater would have been extremely short and extremely undignified! It would have consisted of the words "Get out!!" at a very high volume...