I have a lot of thoughts on this but not sure any answers... To me, overall, it is more about McVay than personnel. And I LOVE McVay, obviously. But (even going back to his three years in Washington) he has netted mediocre red zone scoring results. Now, the Rams have scored over 1,000 points in two seasons so I'm not complaining... But to the arguement itself...
Now are there other factors at play? Sure. Do they get more conservative in the red zone when they've had bigger leads (which has happened a lot)? I don't know those actual numbers, but probably.
Like you said, Gurley has been their main red zone threat. I thought Reynolds and/or Everett/Higbee, given their size, could become that. Maybe one still could. You need some physical mismatches in the red zone (like New England had
for years with Gronkowski).
I also think part is simply Goff's continued development. Being a great red zone QB is probably one of the last things to be able to master. He had 23 TDs in the red zone last year- but also 4 INTs (only Roethlisberger and Keenum had more). The year before he had 23 TDs and 0 INTs. He hasn't surpassed 60% completions in the red zone yet as a pro.
So I think it's just step improvements between McVay's play calling and Goff as the trigger man. Again, they're not bad. They're just 'middle of the pack' with an otherwise elite offense (so it stands out). They were 42/74 in the red zone last year. Being 48/74 (converting 6 more) would have had them 8th in the league vs. 19th. 46/74 13th.
Could they draft a guy that maybe could be that physical red zone mismatch they don't seem to have at WR or TE? Sure. But I don't think that changes results much.