Kupp's been instrumental to this offense since he settled in. Every stretch of games we haven't had him this offense is a completely different beast. If you go back to McVay's days at Washington he had a very similar pass game threat at TE (incidentally similar to Kupp in size and weight), though as good as Jordan Reed was he was not in Kupp's class. So way I see it McVay requires a slot/middle of field threat to be at his best as a play caller. And in Kupp he found a player who went above and beyond his scheme in his gameday awareness, recognition of coverages, and overall scheme mastery.
If we had Kupp in that first Super Bowl we would have a title under our belts. Because the Patriots barely beat us as it was, but Kupp would have torched that gameplan and forced them to adjust. Belicheat admitted he had planned on being forced out of the gameplan but it never happened. That was because our WR/QB combo was not good enough. But if Kupp was there I am confident it would have been.
IRT contracts the Rams have their strengths and weaknesses. They are quite average in their signing of FAs overall, as this past FA season can attest. Not special by any means. But they are good at paying the players who deserve it, among whom Kupp is included. And they are also good at structuring deals to cover them if things go south. Which, incidentally, they have an out with Kupp after this season.
What is interesting is McVay prioritized what would have been Kupp's replacement in trying to move up for Bowers in the last draft. Because Bowers is basically a bigger Kupp. LaPorta would have been the same, in terms of filling that role for McVay. So I think the Rams are not stupid in this issue. And I think they are going to keep trying to replace him in the draft, because they are aware his style of play comes with injury. Lastly when I say "replace" that isn't to mean it would happen immediately. Like for example if they had drafted LaPorta or Bowers, two ideal fits over the past two drafts, either would undoubtedly have been quickly worked in as TEs in most of their their snaps with Kupp on the field with them.